There is a white plastic bar at the back of the buckle, that can be pried out (since you are discarding it, do not worry about damage). You can then remove the crossbar, and subsequently the belt.
The metal buckles can be taken apart by prying with a screw driver a the "square" end. It is difficult, and holding it carefully is important, so that you do not stab yourself in the hand. Once you get the top off, you can reassemble it with the belt in place. With the angled top part over the front of the bottom, and the square part on top of the rear, I have put a cloth on top of it, and stomped on it with a rubber heel shoe. It should just pop back into place. If you want me to take some demo pics, send me your email.
If you have a tan interior, and would like to keep it stock, I have some tan plastic capped buckles in excellent condition.