For some rabid R/C’ers out there, when it comes to aircraft, grossly overpowered is sometimes just barely enough. There are many people who like to see just how far they can take their models and don’t always know where to go to get the kind of information someone would need to understand what CAN be done when you are wanting to “beef” up your R/C.
Because this is kind of a broad question with specific answers depending on the kind of R/C your working with, I will try to be as helpful as I can. In general, there are here are three factors to keep in mind when modifying an aircraft. First, know the weight of your plane. Second, know what type of flying you will want to be able to do. And third, make sure you have enough prop clearance.
When you start overpowering an aircraft and put in a bigger motor, it requires a bigger prop. These three things will determine whether you will need more wing area for slower, more stable flight; whether you need a larger engine with a more powerful battery so you can do more aerobatic type maneuvers; or whether you need to adjust to make room for a bigger prop.