Mostly likely,, broken rings, remove fly wheel cover 1st. then Remove 4 nuts on head.Remove 2 exhaust nuts and pull down header clear of cylinder. Try to rotate flywheel forward and backwards if cylinder moves with motion, it's seized or broken rings, most of the time with broken rings. you'll see dents/chucks on the dome of the head As soon as you pull the head. if cylinder slides off piston easy. and flywheel still won't move. you have other issues.
Tools you'll need to check.
A Ratchet driver, 10mm socket and short extension.( For nut removal)
a flathead screwdriver. (for fly wheel cover)