If the amount of aid disbursed to a student exceeds the amount of invoiced, aid-eligible charges, the student's By Term Summary will show an aid overpayment.
You have a few options for aid overpayments: you may refund it to the source, refund it to the student, or retain it to apply to the student's future, aid-eligible charges.
Refunds show up in the Transactions table as Aid Repayments. They credit the associated Liability account and debit the A/R account (increasing their respective normal balances); in the real world, you'd send a check to the aid's source institution or the student.
Read about refunding financial aid (please don't attempt to refund financial aid by recording an outgoing payment—it'll just waste your time!).
Retain for future charges
To retain financial aid for future charges, you don't need to do anything. Aid overpayments become unapplied payments (visible on the student's financial Dashboard); once you invoice some aid-eligible charges, apply that unapplied aid payment to that invoice.