To log out of ProRemote and disconnect from ProPresenter you can simply close ProRemote. If you want to manually disconnect in order to change connections or ensure someone can't accidentally log into ProPresenter, you will need to go into the app's settings.
At the bottom of ProRemote, tap on the "More" button then tap on "Settings".
Scroll down in Setings until you see the "Logout & Disconnect" option. You can also change the Automatic Login option here as well.