I'd like to try a different crank arm length. I'm currently running a 175 on my Trek 5200 which has an Ultegra triple. I'd like to go to a 172.5, or a 170. I assume that I need only replace the right and left crank arms to accomplish this?? If this is the case, how do I do it? Do I need to torque the bolts? Locktight?

ThanX!!!!