i wouldnt try it if i were you. if you don't know the head needs to be removed to change your pistons ur gonna fuck something up. Get some one to do it for you or in the least help you.
...when the pistons are resisting your attempt to come out, hit them with a 40 lb sledge hammer...
...when the rings are catching on the installation because you lack a ring compressor, take the 40 lb sledge hammer to the pistons again, be sure to miss the pistons a few times. If you're still having problems add some more weight to the end of the hammer as well as more surface area, enough to hit the whole block...