Editing barcodes should always be done very carefully. Once physical barcode labels are applied to items in inventory and the barcode number is changed in Katana, these items won't be identified with scanners anymore and they will need to be searched for manually and new barcode labels printed for all of them.
Barcodes can be edited in the following places:
On the item card - Open an item card that has barcodes and click on the barcode field you want to edit and either write or scan a new barcode number. (Internal barcode is checked for uniqueness - if the entered number is not unique a new number needs to be added).
From Stock screen > Batches tab if you use batch tracking. Batch numbers and batch barcodes can be edited in the list.
While receiving a batch trackable item - when barcodes are generated automatically, the new batch number created while receiving items will also generate a batch barcode. The automatically generated barcode can be edited before receiving the item in inventory.
Note: Editing batch barcodes while receiving can be useful if you want to use the same batch/LOT number your supplier wrote on an item, and printing it as a barcode gives you backward traceability to your supplier batch number whenever you need it.