From a tiler's point of view, it is a must to remove the plastic trim if you want to tile upwards. You can cut it with a Stanley knife. Hope it helps. Good luck!
Agree with the comment above sharp stanley knife between the tiles and trim will cut and be able to remove easy. If you want to replace the trim your gonna have to take all the tiles around the edge.
Removing plastic tile trim can be a straightforward process. It is important to note that the specific steps may vary depending on the type of plastic tile trim and the installation method used.