You must mark the note by choosing the marking icon, then tab long in a free space close to the Note you'd like to change. Tap your ipad pen as long on the screen still those grey circles appear, that give the possibility to stretch them with to draw a window that just contains the note you want to change. Its colour changes to orange. ...... Then choose from the icon menue the note length you want to give to that note.
It should change. To confirm you must tap once outside the window you just draw with your apple pen. The colour of the note should change to black again
Thomas Kaulen, Germany