Be careful with any palythoas as they may contain palythoa toxin. If you're going to mess with them, you should use gloves and preferably a mask and goggles. It's also recommended that you don't have any pets or children around when you're messing with these, just in case. It's rare that the toxin gets aerosolized, but there have been stories of people's dogs dying as a result of palytoxin. Not trying to scare anyone, just pointing out the need to be safe when dealing with potential palytoxin.
Most people will say if you can remove the rock from your tank and deal with the palys outside in a separate bucket, that's the way to go. You can scrape them off the rock or cut chunks off the rockwork with bonecutters and then put the rock back in your tank.
Dealing with them inside the tank is trickier. I have that very issue right now as some trash palys have overgrown some prime real estate in my rockwork. I've been removing them during water changes by pulling them with tweezers and having the syphon suck up the removed coral polyp and hopefully any palytoxin it releases. If you're going this route, you should still wear gloves, goggles, etc and run carbon after the water change to help soak up any released palytoxin. I try to only do a few at a time so as to not overwhelm the tank, but I only have about 34 gallons of water volume. Larger tanks could probably handle more being removed.
Another approach is to use something like Aiptasia X, Joe's Juice, Kalkwasser paste or even F Aiptasia. I've heard people have mixed results with Aiptasia X, but kalkwaste paste and F Aiptasia seem to work for people. You just have to be careful not to use too much at one time or get it on any other corals. It pretty much kills anything it touches.
Hope this information helps! Regardless of which route you take, be safe!
