You must have The Bat Home or The Bat! Professional installed.
To install the Beta, just unpack the downloaded RAR archive (you may need the unpacker) and replace TheBat.EXE file in The Bat! program directory. (It is recommended to keep the previous stable .EXE file in a safe place just in case the new Beta causes problems)
As a general safety rule, it is recommended to create a backup before starting a new Beta. We try to keep public Betas as safe as possible, but it is always better to be on the safe side of things.
Internet and communication
3.09.05 Deep Alpha
Product page: here