To change gears on a Schwinn mountain bike, first, locate the gear shifters on the handlebars. There will be two shifters, one for the left and one for the right. The left shifter controls the front derailleur and changes the bike’s chain position between the chainring gears. The right shifter controls the rear derailleur and changes the chain position between the cassette gears. To shift gears, simply use your thumbs and index fingers to push or pull the shifters. Pushing the left shifter towards the bike will make the chain shift up to a larger chainring gear, while pulling the left shifter away from the bike will shift it down to a smaller chainring gear. On the other hand, pushing the right shifter towards the bike will shift into a harder gear, and pulling it away from the bike will shift to an easier gear.