You will need the Connections Settings permission to perform this action.
Click on "Connections" from the left-hand navigation. Afterward, click the "Settings" tab.
Then click the dropdown arrow next to the edit button, and select "delete".
Instead of deleting a connection type, you can instead deactivate it so that new connections cannot use that type. This is recommended to keep historical data. After selecting the type from the drop down, change the "Active?" field to "No" and then hit the "Save" button.