The best option for control is to treat them with kalkwasser. Run a search and you'll find a couple good threads about the method. Manual removal shouldn't be tried--it will result in an outbreak.
We have several in our FO tank. Started out with 4-5, and a year later we have about 7, varying in size from about 1 inch total diameter to well over 6 inches (tentacle diamter, not the disc!) We're getting ready to treat them since they've started to spread a bit more rapidly than we are comfortable with. There's a trigger in there, and he never touches them.
There are a few other options, including a nudibranch that eats them, and of course the true peppermint shrimp. Keep in mind that the nudibranch is an obligate feeder, and will die once the aiptaisia is gone. The shrimp may not be compatible with other tankmates, and can be tricky to verify it's a true peppermint. Other shrimp look similar but will not help with aiptasia.