I suggest you do it at least once a month not only to remove unnoticed viruses roaming around your computer but also to free-up the spaces you might want to use someday.
So here's how I do it:
STEP 1: Kick them out
Go to Control Panel and choose Add or Remove Programs for XP and Vista or Programs and Features for windows 7 users. Review your installed and programs and remove the ones you rarely or even never use. Sometimes I install programs I only use once and then I forget all about them.
Here are some of the things I found and uninstalled:
1. Livestream Procaster
3. Skype Toolbars
4. Nokia Software and Drivers
6. Yahoo Toolbar
8. Ran Online
9. Canon Printer Utilities and Drivers
STEP 2: Chase them away
Go to your computer's Program Files. Usually it is located on Start > My Computer > Drive C: > Program Files or in my case, Program Files (x86). Browse your your folders yet again for softwares you have installed that you want deleted. Some files don't show up on Step 1 above, so you might want to open these software folders and uninstall them from there. Some folders won't have an uninstall option so what I do usually is click on the folder and hit DELETE KEY.
NOTE: Never ever, ever delete a folder that you are not familiar with. It might contain important files for your computer to run. Especially folders which has a string on numbers and letters on it. I know its annoying to have these, but just let it be.
STEP 3: Dust the shelves and organize it
Go back to your My Computer folder. Right click on Drive C: and choose Properties. Click on Disk Cleanup.
Tick all the check boxes and click Clean up system files. Your computer then would analyze how much space this would free (Mine is 1.8 Gigabytes). Next, still on the Windows Properties, choose the Tools tab and and click Defragment now. I hate this step the most because it takes a lot of time.
STEP 4: Wipe them clean
After removing your extra files, run a registry cleaner. Every computer must have one! I use CCleaner for my computer and what it does is wipe the registry clean, especially for softwares which I just manually delete with a highlight and the delete key.
STEP 5: Spritz an air freshener and take a rest
After all that refreshing clean, run your antivirus. I use the free version of Avira Antivir, and it does the job done. Do and entire system scan which usually take hours and hours of waiting. I usually do system scans at night leave mine overnight to finish.
That's it! Goodluck with your cleanup!
If you have anything else to add, some comments or some questions, don't hesitate to leave a comment!
Reese's and Kisses!