Are there restrictions on how to spend the refund money for the American Opportunity Credit?

If you get it, there are no restrictions on how you can spend it.  The confusion may come from the special restrictions on getting the AOC.

There's a new urban myth among college students that says they can get a $1000 from the government just for filing a tax form. For most of them, they simply aren't eligible. A full time unmarried student, under age 24, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You usually must have actually paid tuition, not had it paid by scholarships & grants.  It is usually best if the parent claims that credit. 

You cannot claim a credit if you are, or can be, claimed as a dependent by someone else.

A lot of people are just not eligible. See https://www.irs.gov/Individuals/AOTC