what operating system are you using?

For XP:

Click Start > All Programs > Accessories > System Tools > Click Disc Cleanup
Now launch this utility and click More Options tab. Under which click System Restore and followed by that click Clean Up tab a message will popup -Are you sure you want to delete all but the most recent restore point?Click Yes then OK. Finally another message will popup-Are you sure you want to perform these actions?Click Yes.
Now, all the System Restore points except the most recent one are cleaned. As a result there will be more free space in hard disk.

IIRC Vista is similar

Posted By: Ralf Scrampton, Jan 22, 18:56:50