not too hard, after removing the vacuum pipe and the oil drain pipe, the two nuts, well actually they are bolts, first completely remove the top one then loosen the bottom one with a 10mm combination spanner. the bottom of the vac pump is slotted to allow the pump to be lifted clear of the loosened bottom bolt. take care not to loose the rubber 'o' ring seal. and allow room for the push rod that sticks out of the head.