archive or delete the from temp folders, remove or archive the junk files like video, downloads, songs, jokes, etc. run a check disk and do a defrag. it will boost your computer speed by at least 10%.
GV is right. registry is not for you to mess with. Also, do not delete files from folder that you do not know what they are.
disable norton programs. it offers the worst pc companion as it takes up too much cpu overhead.
ensure there is up to 30% hard disk space left. Also, clean the computer air intake vents. if you can, open it up and do a clean up. with excessive heat built up, your computer can run slower by up to 90%.