Hi Ross

(assuming you are using Ledger 9.x and nothing is posted to period 13)

This is not going to sound easy but the alternatives are worse. First unpost every batch, then export those now unposted batches to a CSV file by using File | Export | Batches, then create a new Ledger with 12 periods by using the File | Export | Clone Company function, and then finally import the CSV file into the new Ledger. It will all come in as one batch but everything will be in the correct period.

This is a bit of a simplification, you'll need to check that the export file has the fields you want to move, and that the import template matches the exported file. But you get the idea.

Steve