ok.. the 'block' contains the crankshaft and transmission.. The 'cylinder' is where the piston goes up and down and the 'head' is the top.
Be careful about knocking things with a hammer. I have seen (i forget where) a cylinder that had one additional, short bolt near it's base that must be removed before the cylinder will come off. The piston can remain attached to the connecting rod.
I get the notion that you will have a few new problems further down this road unless you get some guidance. (Do you know how to compress the piston rings so you can get the cylinder back on without snappping a ring?)
Get a service manual or an owner's manual. You may find a generic small displacement engine manual that covers the QT50 at the Yamaha store.. Whatever you get will be well worth it in money saved and headaches avoided.
well.. since you are breaking head bolts i'll assume there is some corrosion down there on the block, and chances are that your cylinder/block gasket is just stuck.. Thats why it won't slide right off. A bit of gentle prying with a screwdriver should free it up.
While you are out shopping for a manual, maybe go get a torque wrench too.. A small inch-pounds wrench will do for these little bikes.