I myself have limited past experience with any birds (Im more of a reptile addict lol), and pretty much all of my bird knoweledge (which is limited) has come from reading the forums here and stealing good ideas offf those who have more experience lol. I did have a galah for a few years before he escaped). I found that that sprouted seeds were great way to to improve the diet (they are much more nutritious/;less fattening than plain old dry seed) and he went from only really eating the dry crap found in supermarkets to sprouted seeds without any dramas. Having spoken to someone who's had a lot of experience with parrots I learned that alot of parrots are the same. Getting him to eat things like brocolli and other veggies took a bit more effort/imagination. I found that chopping everything really fine and mixing it with plenty sprouted seed/pulses etc meant that it wasnt so easy for the little bugger to pick out all the yummy bits and throw rest of my lovingly constructed master piece all over the avisary floor lol.
One thing a wise long term member once said about changing diet is that it is best not to rush things to much. The bird willl have already gone through a lot of changes which will mean stress so take things slow. A few more weeks on a crapppy diet isnt going to kill them unless they are servierely malnourished.
Hope that helps