If you go into your set up mode, or speaker level adjustment section on your amp, there should be a choice for no center channel, and small center and large etc. Just turn it off,or turn the center volume level all the way off..     Dave

There may also be a switch somewhere on the receiver for something often called "phantom center channel", that when turned on routes the center channel information to the front main speakers.  This often sounds better if you're sitting in the center simply because the main speakers are larger than the center channel speaker, hence better sound quality.

Steve