The small chords above the regular chords are Alternate chords and when editing the song you need to switch to Alternate Chords mode:

iPhone/iPad, Android: tap this button: 

OS X: click on Alternate Chord

Now you can easily add, change or delete Alternate Chords.

Note: the player will ignore the alternate chords (they are used for visual purposes only) but will transpose along with the main chords.