How can I make the front suspension softer for Da Vinci Cameleon?

My boyfriend has a green da vinci cameleon mountain bike and can't get the front suspension to go more than half way down. When we bought it the guy said that the height was good but didn't say that you have to be over 200lb for the suspension to be okay. The things that you can turn to adjust the suspension (I'm not sure what they're called) are at they're maximum softness. Is there anything else we can do to make them less hard? Also the chain keeps on getting off when quickly changing from the 1st to the 3rd front speed. I went to the bike store and he adjusted a screw but the problem reappeared a few days later.