Why can I not uninstall my AVAST Anti-Virus Protection?

I have a free AVAST ANTI-VIRUS application which was on my laptop when I purchased it. It was working fine and the only way to keep it up and running is to update it every time it's about to expire.
One day, I wasn't able to update it when we moved into a different apartment because we didn't have Internet yet. I tried to update it but I couldn't so I decided to just remove or uninstall it but I kept on getting an error message.
How do I remove it completely?
