If the charges have already been billed to the client, the easiest thing to do would be to enter a CR on the matter (through AR Entry) and apply it to client advances.  In the voucher you create for the current month’s statement, enter a negative distribution line charged to the Client Advances Written Off account (DO NOT enter a client-matter number). When you enter the voucher, the invoice amount is entered as the total you owe on the statement. Individual distribution lines are entered for each of the charges. The negative lines are entered for the credits.  The total of the individual charges less the credits should equal the total amount due.

If the charges have not been invoiced, locate the original voucher that created the charges on the client file. Adjust the voucher – remove the distribution lines that created the CA charges for the client-matter and add a new line that hits an expense account. Since the charges have not been invoiced, the voucher adjustment process will delete them.  When you enter the new voucher for the new statement, you will still enter a negative distribution line, but instead of hitting Client Advances Written Off, hit the same expense account you chose to use above (during voucher adjustment).