You cannot delete an Asset, however you can archive an Asset which works in the same way. You are able to archive individual Assets or multiple at the same time.
To archive an Asset, in the Web Portal go to Assets > Asset Register > Select the checkbox for the Asset you want to archive > Select Archive at the bottom of the page. If you would like to archive more than one Asse, you are able to adjust the rows per page, allowing more to select from.