How do you make your face thinner and how do you lose a small double chin?

You can't really spot reduce. Anyone that says you can, without undergoing surgery, is either incorrect or trying to sell you something. So, unless you have cosmetic surgery, you have to lose weight in general and your face and chin will eventually thin out just as it eventually got heavy when you put weight on. One thing you can do though is while going through an overall weight loss program including proper diet, weight lifting and cardio. Drunk plenty of water and stay away from caffeine and salt. A lot of bloating of the body in general, especially the face, actually caused by too little water in the body. The body then holds on to as much as possible...hence the bloating. If you up your water to 8-10 glasses per day, or even more, depending on how big you are, your body will eventually get rid of the bloating and re-balance.

Also, don't worry if you find yourself going to the bathroom for the first week or two after starting to drink a lot. This is natural until your body gets used to you drinking more water than usual.