Hello,
can you, please share with us more information, what versions of our software are you using, what troubles with VPN you are experiencing, what updater is not signed (we sign all what we release, but as always something might go wrong).
All Avast software can be uninstalled usual Windows way. If you wish to uninstall Avast SecureLine VPN, on Windows 10, under "Apps & Features" you should be able to find "Avast SecureLine VPN", chose uninstall and removal should start