I'm almost sure you meant "prove that if a group is NON-abelian then its order is > 5, which of course is true ==> you need to prove all the groups of order <= 5 are abelian. Now, 1,2,3,5 are immediate (right? prime order groups are cyclic...), so the only "problem" is order 4.

Supose then that G = {e,x,y,z} is a non-cyclic group (because cyclic groups we already know are abelian) with 4 elments and play with the elements: for example, what can xy, yx be so that teh axioms of group theory will be fulfilled? Of course, e = the group's unity

Tonio