It depends on the update, honestly. Some of the big ones require a start over, but will still let you start off at day 1, 2, or 3. So if you are in this "in between" area, I reccomend starting the day over or you'll miss some content unfortunately.
Overwrite doesn't destroy your saves. If you uninstall it will wipe your saves. We haven't had to force people to start over in a while but we still have checkpoints your can start from when you start a new game, just in case.
