This can only be done in the backend. if you are not already there, log to the backend control panel of your church website located at www.yourdomainname.com/administrator (where yourdomainname.com is your actual domain name) and go to components>volunteer>ministries OR components>volunteer>interests OR components>volunteer>locations.
This is where you add and remove all ministries, interests, and locations. Use the icons on the right of a specific page (such as the page that comes up when you go to components>volunteer>locations) to add or delete existing items.