You say what you claimed and when it was "for". What you don't say is when you paid it. You can only claim the $4000 for 2015, if you paid for it in 2015. If you paid the full $12,000 in 2014, you cannot claim anything on your 2015 return.
If that is the case, it will be worth while to sort it out. It most likely will not be necessary to amend 2014. Although you may have entered the full $12,000, probably only $4000 ($10,000 if you are a grad student) was actually used to calculate the tuition credit. Review 2014 form 8863
