Well if hes bigger then it stands to reason hes slower so dodge his punches (I doubt there will be many kicks) and weave in for quick jabs to the face and ribs. If hes not much stronger than you then you should be able to take a few hits without much bother. But honestly, if your not wanting to fight just try to walk away.

If you don't want to fight, then don't. If you don't know how to fight since you had to ask how, don't. You don't have to fight, you always have that option.

This guy wants to fight me for unreasonable reasons. I'm big myself weighing 240 but he weighs 340. Don't get me wrong, I don't want to fight him but I need to defend myself if he decides to which is probable at this point. He's not much stronger than me, he may bench about 20 more than me. I know cause he used to be my lifting partner. I'm 15 btw if it matters