Your carriers will likely change their rates at some point, so you will too. Editing and deleting rates and rules is pretty easy in Weebly.
To edit, rename, or delete a shipping area, click the ellipses to the right of the area name:
When you choose Edit, you're taken back into the dialogs where you created the area. Change to your heart's content!
To edit or delete just a rate within an area, click the Edit link for the rate. You're taken back into the shipping rate dialog and a Delete Shipping Rate button allows you to delete the rate.