I don't recommend deleting any vendor credits, especially if they have been on the books for a long time or if they span a wide time frame. By deleting them, you are affecting multiple previous periods and could be causing a world of hurt for yourself by knocking your Trial Balance out of whack. Keep in mind that deleting the vendor credit not only deletes the transaction from the A/P ledger, but also deletes the GL expense account that was used as well as the any tax amounts.
There are a couple of ways to clear vendor credits that you believe should no longer be there, although, I wonder what renders them invalid? If they were a valid credit at one time, why were the credits never used against subsequent bills or reimbursed by the vendor? That's a whole other question that should be investigated.
1) Create a bill that is exactly the opposite of the credit, using the same expense accounts and tax codes, but dated in the current period. Use the 'Pay Bills' window to 'pay' the invoices with the existing credits.
2) Create a General JE with Accounts Payable in the first line, CR the total amount, tab over to 'Name' and enter the name of the vendor. On 2nd and subsequent lines, enter the expense account(s), DR amount, and tax line. When entering taxes in a GJE, use the tax payable liability account, then tab over to 'tax item' field and enter the item code used for your GST/HST ITC's, so that the tax is coded properly to show up on the tax reports. As in #1, use the 'Pay Bills' window to 'pay' the amount you just created with the existing credits.
The easier of the two is definitely #1, but for whatever reason, some people may have their own reasons for adjusting with a GJE instead. Either way gets you the same result.
