You will find a good discussion on CG location at www.rcaeronauts.com.

You should know that the CG must be located forward of the Neutral Point. The farther forward of the NP, the more stable the plane, but the less aerobatic. So, you must also find out where the neutral point is, as well as the CG. The information at the rcaeronauts website should give you an idea of what to do.
Good luck.