It depends on what the lease or rental agreement says. If you break it, it will cost you lots of money.

Is there one available? Do you have a lease? what does the landlord say?

Depends on any lease agreement you signed and whether or not the owner/landlord would allow it

You can ask, they have no obligation to allow it, and your roommate has no obligation to sign you off the lease.

I'm now in a 2 bed 2 bath apartment with my "best friend" and got into an argument to the point where I want to downgrade to a 1 bedroom but in the same complex.. am I able to do that ?