I forgot what version I'm playing. But I'm sure its between B26 and B24.
Also, If I'm playing B24, how will I update to B26?

EDIT: oh and, I got the game from a gifted Humble Bundle, does that prevent me from updating?

The only way to tell if you have b26 at the moment is to look at the installer file you used. If it says "cortex_command-b26-win32.exe", that is b26.

As for updating, if you check back on your HIB page every time an update is released, the new setup file should be uploaded there. It may take a few days though, depending on how fast the HIB people get to switching the file after Data sends in the request.