There's 2 types.
1 type is a real **** to remove, where it has locking lugs part of the plastic insert, that sit inside the metal tubes, the way to release these is to put a thin but strong pick tool to pull the locating lugs outward to release them, done this so many times,
If you get a torch, you can see there's a hole in the tunes of the plastic inserts, you need to put something metal thin strong to push into the hole & push inward to release them, trust me it's not fun.
2nd type is purely released from.the bottom of the tube from the inside of the seats by removing the back cover 1st & then release them from underneath by pushing the locking expanding plastic bottoms inward that allows them to release up out of the tube.