Knubud,
Zack is correct. Drill into the end of the rivet to remove what is peened over and then drive out the rivet with a punch. Save the copper washers that are on the inside for re-use. Unless the stem bands are in very nice shape it may be easier to break them off and install new ones when you get to that point. The old bands, when you try to reinstall them, may still not fit just right with the holes in the wood stems and the holes in the bands not aligning correctly due to the slight difference in thickness of the canvas, filler and paint. An exercise in futility. On the canoe I finished in May the stem bands were already broken so the decision was easy.
Good luck and have fun.
Jim C.