CCleaner is a nice tool to clean up old temp files and clear out registry errors. When running this program, make sure you know what you're checking to get rid of. Here's a nice walk through guide on how to use the program (Click here!).

http://www.ccleaner.com

http://www.filehippo.com/download_ccleaner/

There are other nice FREE cleaning programs out there. I also recommend checking out (1) Malwarebytes' Anti-Malware or (2) Spybot Search & Destroy and (3) AVG free

(1) http://www.malwarebytes.org/mbam.php

(2) http://www.safer-networking.org/en/download/index.html

(3) http://free.avg.com