How to join database user to db_owner role using T-SQL script?

I am using SQL SERVER 2008 R2 Express.

I am working on a new project with a database myDatabase

named db username myUsernamae

.

I would like to use ALTER ROLE

instead sp_addrolemember

because of this post from Microsoft regarding sp_addrolemember (Transact-SQL):

Important. This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work and schedule changes to applications that currently use this feature. Use ALTER ROLE instead.

I tried

USE [myDatabase]
GO

ALTER ROLE [db_owner] ADD MEMBER [myUsername]
GO

      

        
        
        
      

    

but I keep getting this error message:

Incorrect syntax near the "ADD" keyword.

What is the correct syntax?