Hey Eddy,
The link you provided does not seem to work anymore.
I'm in the same position as the OP, I have marshmallow with Avast Mobile Security + anti-Theft. My original SIM card died and I replaced it, but Anti-Theft activates and sends a text to my friend every time I re-boot the phone. My friend is getting tired of the messages and I can't figure out how to get Anti-Theft to like the new SIM, so I figure the best way is to uninstall. But how?
Many thanks for your help!