They're held in place by small clips and you will need to remove the door pannel get at everything. The replacements are longer than you need so you will need to cut them shorter. I use a pair of shears or a bolt cutter to give a nice straight edged finish. The ends are actually notched a small amount to help clear the sliding jaws on the door glass. You should try to carefully remove the old ones and use them as templates.
I always lubricate all the moving parts inside the door when ever the door pannel is off. Something that really isn't done often enough to prevent wear on most cars.
Daniel G Caron