I have three hunter ceiling fans. When I turn off the fans in the living room the bedroom fan goes off. How do I change the codes?

Under Canopy(At ceiling) should be receiver, change codes. DIP switches.
Will also need to change settings on remote.

You change the frequency of the second fan and remote, making sure they still match. The receiver can be in a few different places inside the fan. See:

Ceiling fan remote controls - help and FAQ- Ceiling Fans N More