Hmm, im not realy sure about rings, i need to do it too
What i know is you need to take out the motor i think. To remove the Pisons u need to pop the holes and then release the piston, otherwise u cant change the rings, they are in the middle of the piston. After u take it out and change em u need to RE plug the holes on the side of the engine with those steel plugs. I have no idea how to do it, but i think thats about it. Changing the rings, means u open up engine, open up engine means u have to take off the timing belt and shafts, that means u need to take engine apart, or its too hard to do.
So i dont think its possible to change rings while engine is inside the car, or it will be too hard. Its much eazier to take it out, its quite eazy to work with, its not very heavy. I would also get a NEW full gasket set, and change the MAIN gasket and the oil seals and such if u see any leaks and offcourse change the VALVE STEM seals. Those damn things leak!
I got a kit on ebay with full gasket set, theres also pistons set with a pump check it out. U can also just buy rings, but u still will need NEW GASKETS, engine HEAD BOLTS, and those steel plug things. So its quite complicated. I HIGHLY recommend u do everything at once, you dont wanna be like me, I took out engine to just change the Main Gasket and clean out the Carbon, and now i see i have OIL LEAK, and VALVES leak, and rings leak! Not fun
Goodluck hope that helps