Been there, it's a *****, if you have the hard plastic tube over the stock elbow. The tube goes over a ridge on the stock elbow, that's why its so hard. I just pulled on each with a hand & twisted as I did it. If you are trying to do it with the elbow still screwed down? you may never get it off. Having the elbow detached gives you some wiggle room.
The accufab is just as much of a pain to get in the tube. It needs to go in far enough to lock in also. Plan on some bloody knuckles