AVG free updates or uninstall

I have an AVG free version and I get constant message that the anti-virus is not up to date.  Auto update is turned on and when I try to update manually, it starts and then stops and I get a "general update" error.  after not being able to correct this I tried to Uninstall AGV Free but it won't uninstall - I get a fault message that tells me the "action failed for registry key … : Access is denied.
Has anyone run across similar problems?  Any solutions?
Thanks for your help/