For the piston swap you will need to remove the cam cover, remove both cams, tie the timing chain up so it does not fall.
Remove the head bolts in the sequence specified in the manual, remove the head, assuming you removed the carb and mount that goes to the frame already.
Now remove the cylinder, careful not to scratch it or break the rings on the piston.
Now remove one of the circlips using job specific pliers.
Pull the pin, if its stuck use a socket of the correct size to persuade it to come out.
Install the new piston then the cylinder, set it at TDC, then install the head.
Make sure its at TDC then install the cams with the marks lining up. Now move the ex cam one tooth to go back to Cam-Mod timing.