Hi there,
How to uninstall AVG Free Antivir and install Avast Free on a PC?
Kind regards, Herman
Uninstallers and instructions https://singularlabs.com/uninstallers/security-software/
Or here https://www.avast.com/faq.php?article=AVKB11#
Bobs install guide
https://docs.google.com/document/d/1TCCX0R7AAF2WOxAMQ_kcun2nNnCPFAk2P4RBzFXSgds/mobilebasic?pli=1
Step by Step usually does the job. 
Thank you POndus and Bob3160 for your very useful advice which is highly appreciated by me.
I will go through the process of uninstalling and installing soon.
Kind regards, Herman