You can use TAB or Shift-TAB to move the focus from region to region. Once a region has focus, you can edit as usual (use arrow keys to move cursor) and you can grab the region border with the mouse to move it.
Alternatively, you can select the text region and the overlapping plot with the mouse (both are light blue, then press ctrl to extend the selection (in this case use this to deselect the plot. Then only the text region remains highlighted. In this state you can move it around using the arrow keys.
Martin Kraska
Pre-configured portable distribution of SMath Studio: https://en.smath.info/wiki/SMath%20with%20Plugins.ashx