How do i figure out if i am allergic to adderall and vyvanse (lisdexamfetamine)? i broke out into hives on adderall, but have taken it before and was fine.

One medication ...: Usually i like to change one medication at time , that way if allergic reaction occur , i can figure out what has caused it.

Several options: Allergies are more often to fillers than to the stimulants themselves. You could go to an allergist, who can directly assess whether either of these medications is causing you to have an allergic reaction. You could try vyvanse, (lisdexamfetamine) which is a quite different formulation, even though it produces amphetamine. The fact you didn't have hives before, unfortunately, doesn't mean it's not the cause.