Issueing Credit Notes for the invoices based on downpayments.

I need a process for the below:

1) Downpayment request was issued & paid for 10K

2) DP invoice was issued for 5K rev = zero AR as the DP was applied // and 5K DP remains 3)I need to credit the invoice for 5K (zero AR) and issue a new invoice for 4K rev only and 6K DP remains.

Generally said, I need a process about issueing Credit Notes for the invoices based on downpayments.