you can do it on the sled. you need to get the rear of the sled in the air if possible, or you can lean it to one side and then the other.
at the front of the rails where the hyfax ends you will find a phillips screw. use a good quality #3 screwdriver. these can strip easy and have loctite on them from the factory. align a track window to access the screw and remove it.
take a punch or long screwdriver and using the hole in the old hyfax, or even the hyfax itself, without hitting the rail, drive the hyfax towards the rear.
line up a track window for the hyfax to exit. once you get enough to get a handhold on, you can just pull it out.
clean the rails, apply some lube like wd-40 or pledge to the new hyfax and the rails and reverse the procedure without the punch or screwdriver. you should be able to push the new ones on most the way. take one of the old hyfax and cut a piece about a foot long to use as a driver to set the new hyfax all the way until the screw hole lines up.
sometimes loosening the track helps, i always do. if your track is aligned good now, simply note the number of turns you loosen the adjuster nuts for a reference for retightening.
another shortcut for removal is to simply cut the lip off the hyfax and peel them off. again without causing any damage to the rails.
