Do NOT manually pick them off. They will multiply more than you thought possible. I made that mistake when I first got my tank. "Hmm... I'm just going to twist this bugger off with some tweezers. There that should do it..." WRONG!
Anyway... those are some pretty fine specimens of aiptasia you've got there. A couple things you can do is use a commercial product called "Joe's Juice", or another called "Aiptasia-X". Both seem to do the job quite well - just follow the instructions and turn off any circulation pumps when you're applying the stuff. The other thing you can do is get some kalkwasser and mix it with some saltwater to make a paste and "feed" it with a syringe to the bugger. As it kind of retracts and begins to melt, just kind of cover it with a thin layer of the paste. It won't be back. Do a few each day and eventually they'll be gone. Search the forums here for the keyword "aiptasia" and you'll find many more options for removal.