I guess you mean hard drive space not memory ?
If thats so your probably using xp, that OS sets restore points automatically for you and as your finding out it can eat up your hard drive, download
>>>CCleaner<<< and run that, it will clear all your temp files etc, bear in mind it will clear your cookies as well so if you use cookies to log into sites make sure you know your passwords first, you can set it to leave specific cookies alone if needed.
If that seems to sort you out then go into your control panel and double click on the system icon, then go to the system restore tab and drag the slider bar down until your about 6%, if you have more than 1 drive you will need to highlight each drive in turn and set them all to 6%, that will minimise how much space it uses from now on.