Uninstalling free version of AVG from macbook pro

Hello Alan.
We're here to help.
Which version of macOS are you using?

I have just purchased an upgrade for the free version of AVG on my Macbook pro. When trying to install it tells me to uninstall old version first. When I try to uninstall the free version it states 'uninstall cannot be opened because of a problem' ' check with developer to make sure com.avg uninstall works with this version of mac.os' how do I rectify this problem ?

Hello Alan.
We're here to help.
Which version of macOS are you using?