"You do not have sufficient access to uninstall Avast Free Antivirus"

Hi all,
My main query is now that I know that Avast is not going to help my situation to do with corrupt system files, how on earth do I remove it. I try doing the steps advised and I get this:

Directory Path: Control Panel > Programs > Programs and Features > Uninstall or Change a Program:

Right clicking on both Avast Free Anti Virus and Avast Secure Browser and selecting Uninstall:
aYou do not have sufficient access to uninstall Avast Free Antivirus. Please contact your system administrator"

What on earth do I have to do to get rid of this program. Can anyone please point me in the right direction? Thank you.

Follow instructions: https://www.avast.com/uninstall-utility