As has been suggested above, lots of penetrating oil. May take a few squirts a day for a week. I bought the head remover kit from Snyders that is similar to the angle iron above. The kit is a pair of plates that puts pressure on the studs to lift the head. If you have to, you can torque it down a little, let it set for a while and come back to it. A lot of times it will have raised up with the constant pressure.
Here's the link,
Snyders - Product Cylinder Heads HEAD PULLER KIT A-6010-PX
https://search.app/kB3SUd7gnxCwHduNA