It doesn't matter the type of SIP Trunk you've chosen for deletion: there's only one way to delete a trunk.
First you need to select it in the trunk list. Click on the selected trunk and you'll be taken to the Edit Sip Trunk page. Click on the Delete icon at the bottom of the page to delete the Sip Trunk.
If SIP trunk to be deleted is references by some dialing rules, you will be prompted to also delete or not related dialing rules.