Well, it IS a strange tool.....
There seem to be a couple of ways to actually change the pattern from, say, a wide weave to a tight weave. One way is to make a new blank layer, go to Edit > Fill Layer and choose the pattern you want. Then go to the Move Tool, grab a corner handle and reduce it in size (if you increase the canvas size you could then enlarge the pattern).
Not much good like that, but you could either use the eraser to remove parts or put a Layer Mask on the new layer and do the same.
Another way is with the Pattern Stamp Tool, but on a new layer. When you've put down some of the pattern, you can go to the Move tool and manipulate it - resize, move, rotate etc.
I only just discovered that there are some PostScript pattern files tucked inside the Patterns folder. They can be opened, manipulated, resized etc..... but you can't re-save them. Maybe you wouldn't need to, as long as they do their job and stay in place.
Obviously this really isn't in my sphere of knowledge - perhaps one of those books about creative work in Elements might explain it........ I haven't looked, but I doubt that the Adobe Help files are much use.