In good ol' Haynes manual style...
1) remove all the parts from the old door.
2) assembly is a reverse of 1)
Presumably you've had the new door painted or painted it yourself? It's a fair investment, so you might as well make a decent job of it and change the stuff that needs changing.It seems like a good idea to buy a new door but I can see all sorts of things needing to be bought when they break coming out like window seals etc!