Bye William Sure thing, William. Well, it depends on why you are thin. One thing is clear. You cannot decrease your height to have a differing proportion. So you can only try to gain weight instead.
Weight can be either more muscle, more fat, or both.
Now, some people are ectomorphs - they are genetically thin. And it may be hard to overcome the programming, just as it is hard for mesomorphs to lose weight. There is some programming that determines our shape given what we eat and how much we exercise. And overriding that system is difficult for many. Witness the multibillion dollar diet industry for proof.