yeah partial water changes with lower alk water (obviously).
I would think that the same rules apply to lowering alk as do to raising alk. No more than 1dkh in a day but if it were me, i'd lok to lower it by .5 DKH every 3-4 days until you get to your desired levels. This assume you have alk sensitive corals in your tank.
You would just need to do your calculation on your water volume.