Go to Favorites > Families. Filter for and edit the appropriate family.
From the Edit Family page, go to Invoices > Edit the invoice in question. PRO TIP! The next few screens will say "payment" but this is synonymous with "credit."
From the Edit Invoice/Credit Memopage, click Apply Available Account Credit.
This will take you toApply Credit page. (Right-click and "Open image in new tab" to enlarge)
If you select Apply Today this will apply the total amount to the next payment and will distribute any remaining amount to each subsequent payment date (e.g, if you input $1,000 and the next ten payments are for $500 this will apply $500 to the first and second payments and $0 to any remaining payment dates).
If you select, Spread over Remaining Schedule this will spread the amount you are entering evenly over all of the remaining payment dates the user has (e.g, if you input $1,000 and the next ten payments are for $500 this will apply $100 to each of the remaining payment dates lowering the remaining payment amounts to $400).
After entering the appropriate information click Apply Payment/Refundand you are done!