Strip all the covering off.Put it on a weight loss diet ( remove any wood that is not structurally important).Get light landing gear and wheels.Remove control surfaces and enlarge them 10-20% ,add counterbalances.Double bevel,recover and rehinge to get 45% + throw.Install large,powerfull quality engine that will balance the plane as best possible.Add strong servo's with custom linkages and an aft CG and you should have much better performance
Or you could buy a kit or ARF that has been a proven design