You just re download it and delete the old version. You're saves are stored in the user files so they won't be deleted.
Can i get more details on that?
If your asking about the saves, they are stored at.C:\Users\Your user name\AppData\Roaming\RenPy\GirlsundpanzerProjectIf your asking about updating with the new update file.you extract the zip file in the outdated games folder, and replace all files it asks about.
