turn off water, (to bldg ) or use the integral stops on the valve itself- with a flat screw driver turn clock wise to close each hot and cold side, turn valve on, and use an adjustable wrench on the valve stem, on the wrench flats, on the heavy brass part of stem-apply torque CCW being careful to back up the applied force if necessary. remove slowly so no little parts (if any) spring out. and notice how the part(s) are orientated for reassembly later with new part(s) if needed. re-assemble in reverse order. In doing a repair it always best to have the new part(s) ready to be installed on hand. unless you need the part to take with you to indentify and find parts. but you sound like you have identified the make already that's good if your correct.