Those hammer in, so will be hard to remove in a way that makes them re-usable. You could try getting a putty knife or slot screwdriver under the head and prying, but you'll probably make a mess of it.
I've found that the nice people at the Ikea parts counter are pretty good about providing replacements if you show up with the old part (and, as you have, the part number).
Most of the time you can chisel it out with a scratch awl and a utility knife. You will dull the blade of the knife, but that's why they are replaceable. I also would use my $2 awl, not the heirloom one with the rosewood handle.
Knock out the drywall around it until you can grab it with locking pliers. Either unscrew it or break it off (if it broke going in it may not want to come out any more cooperatively.) Spackle the hole and move whatever it is that caused you to drill it up or down a little bit so the new hole does not line up with the old one if the screw is broken off in place.
Best Answer
Those hammer in, so will be hard to remove in a way that makes them re-usable. You could try getting a putty knife or slot screwdriver under the head and prying, but you'll probably make a mess of it.
I've found that the nice people at the Ikea parts counter are pretty good about providing replacements if you show up with the old part (and, as you have, the part number).