Help fixing Vermont Casting Winter Warm Insert

[Beac]

Last winter, I received a crack on the right side of firebox. I ordered and received the replacement part. I decided today was the day I was going to fix it. I removed all the trim and I tried to discount it from the chimney insert. I removed the thin metal plate from the top of the box, and removed the four bolts on the flange on top of the stove. I can not get the flange to slide over the chimney liner, nor can I get the flange and liner to clear top of insert so I can slide the insert out to replace the part. Suggestions. please