No, don't delete the old version.
And since this game can't really get in any appstore, you have to update it the hard way.
Which is, download the apk of the new version and install it on top (as an update for) the old one.
NEVER, uninstall the game, you lose your savegames that way.
You can backup them if you have a good file manager that can go to
Android/data/com.domain.corruptedkingdoms/files/saves
Solid Explorer is recommended.