removing headrest adjusters??

I have a fresh set of seat covers that i'm trying to put on some seat frames. the new covers have plastic trim at the top of the covers, but i can't tell how to get the old plastic trim pieces off. Any advice?

Just to clarify I'm talking about the black adjusters that need to be turned to move the headrest up or down. How do you get those off without breaking them?

Those pieces fit into a round slot on each side and have a tab that holds them in place. What I do is lift the seat cover off from the bottom (easy to do but be careful when pulling the fabric away from the foam as it is held in place by velcro strips and will tear off the foam if you aren't careful) and once it is clear (kind of like pulling your shirt over your head) you can get pliers or a screwdriver to push those tabs in. If you try to yank them out, they may break

HTH
Todd