Alpine ski pole baskets are usually attached to the pole tip with a Snap-fix or Snap-on system, which means that they are pushed onto the ski pole basket adapter or ski pole ferrule, that have a special narrower part where the basket snaps into place.
To remove the basket some tools and force is needed and some cases they need to be cut of the pole tips with a Stanley knife. Worming up the basket (up to 50 °C) prior removal also helps a lot.