Editing a puzzle
Adding items On the left side of the network window are a bunch of toggle-buttons. If you click on one of them, that one is selected. Now, click on the network and that device will be placed where you clicked.
Deleting Items If you right-click an item, you should have a context-menu allowing you to delete that particular item. If the item is locked (edit -> options -> net-tests) then you will not be able to delete it until all the tests referencing it are removed.
Moving Items You can drag items around on the map. You can also select multiple items (drag a select box around them) and move a bunch of them at a time.
Editing Items You can right-click an item and "edit" it, or you can double-click an item to edit it.