If the app is crashing consistently on a certain level or when it starts up, it's very likely that some of the assets you downloaded when you were installing or updating weren't downloaded correctly. Uninstalling the game and re-installing it will usually fix these types of crashes.
On Android, some devices may take a while to fully erase the game files before you begin re-installing. If you have an application manager on your device, try using it to make sure that all of the game files have been completely removed prior to re-installing the game. Restarting your device can also ensure that the memory has cleared these files, or just wait a little while before re-installing the game again.
You will want to make sure that you are using a stable WiFi connection to download the game again where possible. Most of our games can have relatively large downloads, so doing this will minimize the chance of experiencing connection issues which may corrupt game data as it's being downloaded. If you're using Android, the game will need to remain open while installing or launching it for the first time; it may not install correctly while running in the background.
If you have the option, remember to back-up your save data to the Cloud (have a look at our other articles for instructions on these features for specific games) from the in-game settings menu so that you can restore it later without losing your progress; uninstalling an app will usually erase your local save data along with the app so that it can re-install clean. You will want to make sure that your latest progress is available on the Cloud for you when you're ready to do this, if possible.