why you want to stretch your leather jacket if it'small in size, do change or return it. if you willing to stretch it, go ahead but it'll damage or looks more funny than before.
That depends. Skin by default is stretchable to an extent the tanning process however makes the hides less elastic. Sometimes they are slightly stretchable (usually only in one direction) but normaly not. That's why leather is used for durable garments in the first place. The only possible sollution I can think of is to go to a professional shoemaker which there aren't many (aside the big commercial ones) they have sollutions that make the leather formable for a short amount of time. As they do to shape the parts of the shoe. In general however, I am sorry, but I am afraid there is no way to sretch leather without damaging it.
