|Are you asking about WinXP or WinME? Regardless, all you have to do is disable System Restore, then reboot...all the restore files will be deleted.|
If you have WinME, I recommend that you leave System Restore disabled. It doesn't work well & hurts system performance. If you have XP, it's up to you. Personally, I don't use it, but if you feel you need/want it, you can adjust the percentage of drive space dedicated to the restore files by using the "slider". Immediately afterwards, you should create a new restore point.
XP System Restore