How do you remove and change the oil in a 1985 Yamaha Riva Scooter 200cc?

I have a 200cc Yamaha Riva scooter and have gotten tired of paying someone to change the oil and filter on it. Figured I would do it myself. So any help will be great.How do you remove and change the oil in a 1985 Yamaha Riva Scooter 200cc?See the link - There are pictures attached.