Motorcycle seats, unlike bicycle seats, can't be raised and lowered at will. You can, however, slightly lower a motorcycle seat by removing some padding. About two inches can be gained, which might be good enough. Removing some seat padding has no noticeable effect on seat comfort when riding.
Remove the seat from your bike. Use a socket wrench to remove the securing bolts and then ease the seat backwards towards the fender, sliding it up and out at the same time.
Place the seat upside down on your workdesk and remove the staples holding the covering in place using a screwdriver. Discard these staples.
Mark a line on your seat's padding, delineating how much of the foam you intend to remove. It is best to exercise caution here. You can always remove more later if needed. Adding height again will be considerably more difficult.
Secure the seat in a vice and saw through the foam using a hacksaw. Sand down the top of the seat to remove any uneven or jagged edges.
Remove the seat from the vice. Stretch the old cover back over the seat and use your staple gun to staple it into place on the seat's underside.
Push your shaved seat back onto the bike and secure into place using the bolts and socket wrench.