Plan cylinder head

servus, I have a question: and I am not satisfied with the performance, is logical at 55ps. and I would like to have my cylinder head planned. however I have to know how much to take away whether 0.1 mm or 1mm or whatever with it is not too exaggerated and it is the motor after 20km around the ears skin! besides, is the difficult to expand the cylinder head?? mfg weisi