Helpful info to have: What are you installing on.
Normally updates for android are simple. You Download them and run them. They find the already installed version and add/change what needs to be updated. NORMALLY the saves still work and you can load them the next time you play from the load menu in game.
Sometimes some glitch happens or the creator upgraded some tool and it needs a full wipe and a fresh install. They normally will tell you if that is the case. Depending again what you are playing on that is also an easy fix. Find and copy the saved game folder and put it back after the new install. It varies per platform so I'm not giving details till I know more.