Please follow below steps for admin end: Go to the WooCommerce tab—> Coupons, here you’ll find list of coupons Check/select the required coupon to be deleted.
Go to the drop down “Bulk Action” and select “Move to trash” option and then click on “Apply” button.
If you want to delete this coupon permanently, go to the Trash link and hover to the coupon code and from here you can delete that coupon permanently.
For Deleting coupons at customer side: We cannot provide this facility to the customers because if they can delete the coupon, how can admin track each generated coupons details. So only admin can delete the coupon code.