either from a menu setting within the app itself, or you can go to
Settings/apps/app mgr/Downloaded/name.of.app if it is an app you downloaded and installed
If it is not there, then slide the screen to the left and look in the other columns.
./././ALL will find all the apps mixed in with other processes
./././Running will find that particular app IF you have it activated and running
Once you find the app name, click on it and then Uncheck Notifications