>FWIW the SQL Server 2008 R2 Express is now available for DL. They have upped the limit to 10 gb.
>
>The DL will also upgrade existing SQL 2008 Express installs to R2 which comes in handy.
>
>A client using the new R2 sent me a BAK file and I couldn't restore onto my SQL 2008 developer but upgraded an Express server and it worked fine.
>
>It showed my developer server in the upgrade wizard as well but I didn't have the courage to see if it would upgrade that one. Anybody know if it works?

You can upgrade Express version to Developer's R2. I had Standard version of SQL Server 2008 and I uninstalled it and re-installed Developer's version R2.

I think un-installing/re-installing even in case of the same version will be a safer bet.

Take a system backup using Windows backup before the process.