OK, here's some pics.......
This is the stock wheel for my wagon, I assume you have the same
You first need to remove just the center part with the emblem
The center piece 'just' snaps in place. May take some force, but don't use too much as the tab(s) may break
To remove the full center piece to gain more access, remove these three screws
Clear enough? The thin grip drove me nuts, so I replaced the wheel with this wheel off a '77 Fury
Its not as thick as a tuff wheel, but it is easier to grip and is a little smaller in diameter too. Its a simple a cheap alternative to the stock skinny wheel.
Hope this helps.