R Reset Library Path

I am running Windows 7 and changing one of the path variables that ran where R installed my packages. I tried following this answer on StackOverflow question but accidentally installed it in a directory for which I don't have the proper permissions to get this error:

Error installing package: Error: ERROR: no permission to install to directory 'C:/Program Files/R/R-3.1.2/library

      

        
        
        
      

    

There is a default reset anyway where R installs those packages. The problem is, I've never worried about where it was before, so I can't manually set it back to where it should be.

Thank!