We update the OpenStreetMap data in our app with almost every new release. After you install new update of the app, if update for maps is available, you will receive a notification and could see the red dot on the menu button.
Tap the menu button → Download Maps
You will see list with downloaded maps. You can update all downloaded maps at once by pressing Update All button or update each map (country or region) manually by pressing yellow update icon.
Note: you are not forced to update maps – MAPS.ME continue to work with previously downloaded maps. The only issue is that you can not see map changes and improvements.