Remove Malicious Programs
It is important that you use up-to-date security software to detect and remove malicious programs. Virus programs can slow down your PC and cause unwanted behaviour, even damage to your data.
Spyware tracks your movements on the Web for advertising purposes, but can affect your PC's performance as well. Use anti-spyware programs to remove it.
Clear Out Junk Files
Any time you visit a web site, your computer needs to download the page along with any pictures displayed on it. To prevent your computer having to download the same files again each time you visit the same web site, your web browser will keep a "cache" of stored files it will retrieve if the site hasn't changed since your last visit. Although this means web pages appear faster, over time your cache can eat up a lot of disk space and slow your PC down.
Whenever you delete a file, it is moved to the Recycle Bin first, to give you the chance to change your mind. But the Recycle Bin uses disk space too, so if you leave lots of files in there you are wasting precious space.