Each individual panel on the Taxonomic Editor can be resized using the mouse; as you point the mouse arrow on the join between two panels a double-headed arrow will appear. Simply press and hold the left mouse button and move the mouse until the panel is in the desired position and release the left mouse button.
The entire Taxonomic Editor can also be resized in this way. It also has the standard minimise, maximise and exit buttons at the top right of the window.