Changing the names of field labels in a subpanel

I’m currently trying to change the labels of field under the product module. When I click a product, a “purchased” subpanel appears. However, I changed the name of that to “items” and now i need to change the field names to custom ones.

I need to change the names of these fields to things like “Width” and “Height” but they don’t provide any fields like this in sub panels. I tried creating a new field but it didn’t pop up in subpanels.

Any help would be awesome, thanks.