Tighten it down and loosen it off and use gentle tapping where possible with a big rubber mallet, if this fails get an engine crane and suspend the engine from the cylinder head and continue the tapping, if this fails I made a plate that you can fasten to the head and using 8mm bolts screw the head off. There is a section in my posts on S1 resto. If the head gets out of alignment even with no gunk and corrosion down the stud holes it will jam and you will need to level it up before you try to move it.
Clarkey