Hi my friend,
From memory, when you have the style selected, press edit. From there everything is menu driven. I think you 1st have to select copy, then browse to the style you want to copy from (left hand side) & the rest will follow.
Note, if you search for the style to be copied from i.e. under Ballads, to go to the next style page just press Ballad again. Do this until you find the style. Apart from this, everything else is standard. Remember to select global from the top of the style editor screen as you want to copy all parts at once to your new style.
No need to worry about bar lengths, because you copy everything the Audya will take care of it.
Make sure you'll fly forever!