Whether you can delete an order depends on the User set on the order and on your role's delete rights. If your role doesn't allow it, you get the message Couldn't delete the order.
Delete rights are set per role in the Delete column: the Opportunity row for open opportunities, and the Order row for orders and lost opportunities.
- None: you can't delete any.
- Only own: you can delete only the ones where you are the User.
- Role: you can delete all the ones you have access to.
A user with Team leader turned on can also delete the orders and opportunities of everyone in their own role and the roles below it, whatever the Delete setting.
Administrators can delete all orders. To delete a colleague's order, ask your Administrator to delete it for you or to change your role's permissions.