How to Remove Windows Server 2008 R2 Serivce Pack 1 (SP1) Backup Files

Warning: As a result of removing the backup files you will not be able to uninstall SP1 anymore.

Steps:

1. Make sure the "Desktop Experience" is installed.
   (Note that if you need to install it, it requires a restart and it takes some time to install on the next boot)
2. Run "Disk Cleanup" (cleanmgr.exe)
3. Click on "Clean up system files"
   
4. Select "Service Pack Backup Files"
   
5. Click "OK" to start the cleaning (it can take quite some time, but will give you ~ 1-2 GBs)