If you have a campaign in progress, or want to keep the old version while trying out this one, simply rename the old BOTET folder to something like BOTETold, then install the new one with the folder named BOTET. If you want to play the older version, rename the newer version something like BOTETnew and change the older version from BOTETold back to BOTET. Whichever folder is named BOTET is the one that will launch.