To reorder notes in a stack, you first select the notes you wish to shift, and then drag them to a new location.

To select notes, simply tap and hold down (long tap) on a note. It will begin to jiggle indicating that it is selected. You can tap other notes to select them as well.

Once you have selected the notes you wish to shift in the stack, tap and drag any of the selected notes, and lift your finger up when you reach the new location.

To deselect notes, tap on the background of the notes browser.