Open to the "Settings" menu in the game, tap on the Notifications button to change the status of the Notifications.
You can also turn off your Notifications on the system level:
Android/Amazon
1. Open the 'Settings' app
2. Tap on the 'Apps' entry
3. Scroll down to Alien Creeps TD
4. Disable the 'Show notifications' option and this will stop you from receiving notifications
If you change your mind and wish to continue to receive notifications, all you need to do is enable the 'Show notifications' option for Alien Creeps TD.
iOS
1. Open the 'Settings' app
2. Tap 'Notifications'
3. Tap 'Alien Creeps TD'
4. Slide the 'Allow Notifications' toggle to the 'Off' position
If you change your mind and wish to continue to receive notifications, all you need to do is enable the 'Show notifications' option for Alien Creeps TD.