Search it on you tube, I found that scrubbing bubbles foam works well, yes the bathroom cleaner, if not use a cleaner of your choice Dawn works well also. White towels (available at Costco or any auto parts store) for really soiled seats use a brush, or micro fiber towels not to course. After you scrub them use a good leather vinyl conditioner. Its like cleaning your hands and using moisturizer afterwards. If your not sure of these methods like I mentioned before YouTube it.
Also little tip- a Power washer and degreaser works miracles on the seatbelts.