I hope you're having a fantastic Friday. As @brconsultingid2 mentioned, you won't be able to delete the item if it's been used on at least one transaction. You can make it inactive in your Inventory Center by following these steps:
Go to your Inventory tab and press Inventory Center.
Find the item you need to make inactive, right-click on it, then choose Delete Item.
In the pop-up box, hit Make Inactive, then push Yes.
That's all there is to it. Now your item won't appear in your Inventory list.
If you have any other questions, just hit the reply button below and I'll be glad to help. Enjoy the rest of your day!