Labels can be deleted and updated in ReadyToShip but only before they are submitted to the carrier in a manifest. Changing manifested orders will usually require some interaction with the carrier outside of ReadyToShip.
If an order has not been manifested
Sometimes after you have generated labels, you may find one for an order that can't be shipped.
If the label hasn't been manifested yet, you can delete it by expanding the order and clicking the Delete Consignment button at the bottom right of the order window.
For example in eParcel :
If an order has been manifested
Once an order has been manifested, ReadyToShip can't alter the manifest, and therefore cannot delete the label you produced for it.
If you need to alter a manifested order, you should contact the carrier and ask them to adjust the manifest for you.
For carriers that don't have a Manifest step in ReadyToShip labels are usually generated in the carrier's labelling system outside of ReadyToShip. In this situation, you can contact the carrier or log in to the carrier portal to see if you can remove or cancel the label there.