In general you probably don’t need to be deleting product types. If you do need to clean them up, you really want to make sure that you’re deleting any products. When you removed a Product Type, you will also remove any products that are currently using that product type.
At the bottom of any product type, there is the delete section. This also shows you the number of products that are currently utilizing this product type.
To delete, you would enter your password, and click delete.
If you have any trouble with this, or have any questions, please reach out to support for assistance in deleting product types.