How to delete old subscriptions

Below is a list of all subscriptions / schedules / when they were created / when they were last completed (sorry for lack of attribution)

you can use it to find where the subscriptions you want to reset and manually go and remove them using @Kavins routes

--SSRS SUbscriptions

USE ReportServer
SELECT AgentJobName = sysjobs.NAME
        ,DataDriven = Case when subs.DataSettings is null then 0 else 1 end
         ,Recurrence = CASE WHEN recurrencetype = 1 THEN 'One off'
             WHEN recurrencetype = 2 THEN  'Every '+ CAST(MinutesInterval AS VARCHAR(4))+' Minutes'
             WHEN recurrencetype = 3 THEN 'Every '+ CAST(DaysInterval AS VARCHAR(4))+' Days'
             WHEN recurrencetype = 4 THEN 'Every '+ CAST(WeeksInterval AS VARCHAR(4))+' Weeks'
             WHEN recurrencetype = 5 THEN 'Monthly'
             WHEN recurrencetype = 6 THEN 'Month Week' END
         ,Schedule = ISNULL(CASE
             WHEN daysofmonth = 1 THEN '1st Day of'
             WHEN daysofmonth = 2 THEN '2nd Day of'
             WHEN daysofmonth = 4 THEN '3rd Day of'
             WHEN daysofmonth = 8 THEN '4th Day of'
             WHEN daysofmonth = 16 THEN '5th Day of'
             WHEN daysofmonth = 32 THEN '6th Day of'
             WHEN daysofmonth = 64 THEN '7th Day of'
             WHEN daysofmonth = 128 THEN '8th Day of'
             WHEN daysofmonth = 256 THEN '9th Day of'
             WHEN daysofmonth = 512 THEN '10th Day of'
             WHEN daysofmonth = 1024 THEN '11th Day of'
             WHEN daysofmonth = 2048 THEN '12th Day of'
             WHEN daysofmonth = 4096 THEN '13th Day of'
             WHEN daysofmonth = 8192 THEN '14th Day of'
             WHEN daysofmonth = 16384 THEN '15th Day of'
             WHEN daysofmonth = 32768 THEN '16th Day of'
             WHEN daysofmonth = 65536 THEN '17th Day of'
             WHEN daysofmonth = 131072 THEN '18th Day of'
             WHEN daysofmonth = 262144 THEN '19th Day of'
             WHEN daysofmonth = 524288 THEN '20th Day of'
             WHEN daysofmonth = 1048576 THEN '21st Day of'
             WHEN daysofmonth = 2097152 THEN '22nd Day of'
             WHEN daysofmonth = 4194304 THEN '23th Day of'
             WHEN daysofmonth = 8388608 THEN '24th Day of'
             WHEN daysofmonth = 16777216 THEN '25th Day of'
             WHEN daysofmonth = 33554432 THEN '26th Day of'
             WHEN daysofmonth = 67108864 THEN '27th Day of'
             WHEN daysofmonth = 134217728 THEN '28th Day of'
             WHEN daysofmonth = 268435456 THEN '29th Day of'
             WHEN daysofmonth = 536870912 THEN '30th Day of'
             WHEN daysofmonth = 1073741824 THEN '31st Day of'
             WHEN daysofmonth = 8193 THEN '1st and 14th day Day of' END
             ,'')
            +
            ISNULL(
            CASE WHEN Month = 4095 THEN 'Every Month'
             WHEN MONTH = 585 THEN 'Jan,April,July,October'
             WHEN Month = 1 THEN 'Jan'
             WHEN Month = 2 THEN 'Feb'
             WHEN Month = 4 THEN 'Mar'
             WHEN Month = 8 THEN 'Apr'
             WHEN Month = 16 THEN 'May'
             WHEN Month = 32 THEN 'Jun'
             WHEN Month = 64 THEN 'Jul'
             WHEN Month = 128 THEN 'Aug'
             WHEN Month = 256 THEN 'Sep'
             WHEN Month = 512 THEN 'Oct'
             WHEN Month = 1024 THEN 'Nov'
             WHEN Month = 2048 THEN 'Dec' END
             ,'')
            +
            ISNULL(
            CASE WHEN DaysOfWeek = 1 THEN 'Sunday'
            WHEN DaysOfWeek = 2 THEN 'Monday'
            WHEN DaysOfWeek = 4 THEN 'Tuesday'
            WHEN DaysOfWeek = 8 THEN 'Wednesday'
            WHEN DaysOfWeek = 16 THEN 'Thursday'
            WHEN DaysOfWeek = 32 THEN 'Friday'
            WHEN DaysOfWeek = 64 THEN 'Saturday'
            WHEN DaysOfWeek = 62 THEN 'Monday - Friday'
            WHEN DaysOfWeek = 120 THEN 'Wednesday - Saturday'
            WHEN DaysOfWeek = 126 THEN 'Monday - Saturday'
            WHEN DaysOfWeek = 127 THEN 'Daily'
            END
            ,'')
         + ' '
         + CAST(DATEPART(hh,s.StartDate)AS VARCHAR(2))
         + CASE
            WHEN LEN(CAST(DATEPART(n,s.StartDate)AS VARCHAR(2))) = 1
            THEN ':0' + CAST(DATEPART(n,s.StartDate)AS VARCHAR(2))
   ELSE ':' + CAST(DATEPART(n,s.StartDate)AS VARCHAR(2))
   END
        ,IncludeReport
        ,ReportFormat
        ,c.Name
        ,c.Path
        ,subs.DESCRIPTION
        ,subs.laststatus
        ,subs.lastruntime
FROM msdb.dbo.sysjobs
INNER JOIN  dbo.ReportSchedule rs ON sysjobs.name = CAST(rs.ScheduleID AS VARCHAR(255)) 
INNER JOIN  dbo.Schedule s  ON rs.ScheduleID = s.ScheduleID
INNER JOIN  dbo.Catalog c ON rs.ReportID = c.ItemID
INNER JOIN Subscriptions subs ON subs.SubscriptionID = rs.subscriptionid 
INNER JOIN (SELECT      SubscriptionId, 
            IncludeReport=CASE WHEN SUBSTRING(ExtensionSettings,CHARINDEX('IncludeReport',CAST(ExtensionSettings as varchar(MAX)),0)+27,4) = 'True' THEN 'True' ELSE 'False' end,
            ReportFormat=   CASE WHEN SUBSTRING(ExtensionSettings,CHARINDEX('IncludeReport',CAST(ExtensionSettings as varchar(MAX)),0)+27,4) = 'True' 
                            THEN SUBSTRING(ExtensionSettings,  --field we are searching for
                                            CHARINDEX('RenderFormat',CAST(ExtensionSettings as varchar(MAX)),0)+26,  -- starting position
                                                CHARINDEX('</V',ExtensionSettings,CHARINDEX('RenderFormat',CAST(ExtensionSettings as varchar(MAX)),0)+26) -- length
                                                    -(CHARINDEX('RenderFormat',CAST(ExtensionSettings as varchar(MAX)),0)+26))  END

            FROM Subscriptions s
            )Attachments ON Attachments.SubscriptionId = subs.SubscriptionId
ORDER BY c.Path,CAST(subs.DataSettings AS VARCHAR(3)),recurrencetype