To delete orders in different status, you may find the solutions according below.
Deleting draft orders
To delete a draft order, go to Sales > Orders > Draft tab > choose a draft or click on Select button to include all drafts > click on grey button to Remove draft.
Deleting pending orders
To delete a pending order (Open for buyer or Open for brand status), click on PO number to enter and change the order status as Canceled first, then click on Delete button to proceed.
Deleting confirmed, invoicing, and closed orders
To delete a confirmed, invoicing or closed orders, click on PO number to enter and change the order status back to Open for brand first, then put the status as Canceled and click on the Delete button to proceed.