You should have an option to update the arma beta patch within commander from memory. Also it is the latest updated version, 0.9.1.113, just released two days ago. Since the death of Gamespy it is all Steam oriented.
I would hit the dayz forums Mod section
HERE and i am sure Kichi or one of the crew would help you out pretty quickly.
Otherwise try this, just posted 28th July by DayzJarHead
Prequesites
1. Update your DayZ Commander.
2. In the Settings, tick "Play using Steam"
3. Open Steam - Game Library and right-click on Arma2 OA, --> Properties --> Beta --> Select "beta -"
4. On "Local Files", check your game files for inconsistencies
5. Close and restart Steam, Arma2 OA should now have [beta] behind it in the Game Library
6. Download and install the mod via Steam (search for "DayZ Mod", should be the first in the results)
7. Right-click as you did on Arma2 OA and join the beta for DayZ Mod as well (1.8.1)
8. Restart Steam. DayZ Mod in your Game Library should now have [1.8.1]
Now you should be able to
Connect via Steam:
1. Start the mod by double-clicking "DayZ Mod [1.8.1]" in your Game Library.
2. Have a server IP and port at hand... e.g. 178.77.65.159:2325 (my own server, shameless me)
3. Select Multiplayer --> Remote --> Enter IP and Port... Server should be listed now.
4. Join server by double-clicking it.
Connect via DayZ Commander:
1. Just select a server, e.g. 178.77.65.159:2325 (my own server, again shameless me)
2. Pray that it works. DayZ Commander is a little buggy for me at the moment, although most people on my server connect via DayZCommander
That´s all I have.