You can only morph between presets that uses the same LED, 1/4, 2/5 and 3/6.
I think If you plug in an expression pedal, you will find it very intuitive - you'll see the LED change color and indicate where you are in-between the presets. There is no special way to activate the expression pedal - just plug it in and it will morph between the current preset and whatever is saved on the same spot in the other bank.
After 10 minutes of rearranging my sounds, the morphing option worked like a charm. Thank you very much!