Firstly, check out for the name of the package you want to remove:
dpkg --list
Remove the given package:
sudo apt-get remove package_name
Purge any related code:
sudo apt-get purge package_name
Finally, do a clean so you check everything is correctly removed:
sudo apt-get clean
Or just use this all-in-one command:
sudo apt-get --purge remove
where <package> is the name of the package you want to uninstall. Once done, follow our installation guides to install a fresh copy of Mysterium's software.