In your chosen operating system (Windows/Linux/etc.), you will be aware that at any one time there will be one active window that sits above the others [right now, I'm guessing it's this web browser]. Similarly, in ZeoGraph, there will be one selected filter that sits above the others.
You may use the toolbar buttons and/or menu items listed below to edit, remove or disconnect the selected filter:
You can easily tell which filter is selected because it will be drawn with a highlighted title bar, and surrounded by a blue rectangle, as shown below:
You can change which filter is selected by left-clicking on the filter to be selected. This will change a filter from the unselected state (above right) to the selected state (above left). When you do this, the previously selected filter is de-selected.