Accessories>System Tools>Disk Cleanup.
Then choose your hard drive disk that you use the most (usually [C:]), click OK, it should load the files for cleanup...
A list should show up. (Temporary Internet Files, Offline web Pages, Recycle Bin, etc).
Check the box for Temporary Internet Files, click OK, and confirm by pressing Yes when the box pops up.
(Also: If you would like to individually delete the actual cookies, after checking the box, near the bottom you will see a button that says View Files. Click that and a window will pop up showing you all the cookies that are stored on your computer. Just highlight and delete the cookies you want. Remember: cookies are there to help your computer run quicker but some are unnecessary over a long period of time).
This should clean most of the unnecessary stuff you don't need. Good luck.