Manually Deleting Windows 7/Vista Backup files
Solution 1:
From SevenForuns:
Right click on the computer name of the backup that you want to delete, and click on Open.
If prompted, click on Continue and Yes (UAC).
Right click on the Backup Set YYYY-MM-DD HHMMSS folder
of the backup period that you want to delete, and click on Delete.
Solution 2:
I have for the longest time disliked windows 7's inability to prune older backups. So, I eventually made my own script that does it for me. I also created a simple installer for a scheduled task.
Here it is if anyone is interested: https://github.com/BigRedBrent/WindowsBackupPruning