Is there No way I can decide how much of my payment goes to which loan (part is subsidized, part is unsubsidized). It just seems like I'm not seeing a decline in the balance.
Now, I want to start making bigger payments, but I want to pay off the smaller part first (while still paying minimum on bigger loan) so that I can "see" the difference -- maybe help me to stay motivated. Any ideas?
AES tells me they apply the payment the way they see fit

I'm with AES too. Regardless, there will be a base monthly payment that you'll need to pay on all loans. However, you can pay additional amounts on specific loans by going to the "Make a Payment" screen on your online account and then clicking the tab that says "Specify Loan Payment Amounts."

That's it.