There's really not much to change.
I have been DMing the series straight through (the group just started Heart of Nightfang Spire), and the best way to convert is DIY. This becomes a bigger PITA the further through the series you go (I agonized over changes in the Standing Stones, and the Heart of Nightfang Spire has a very different Redbone, among others). The Sunless Citadel is realllly easy, since there isn't much at all to convert; just run most monsters straight out of the Monster Manual. I'm at work right now, so this is all off the top of my head, but...
***SPOILERS BELOW, SERIOUSLY, DON'T READ THIS. THIS MEANS YOU***
I think the quasit needs some attention, and maybe the druid. You can run this adventure straight away without too much worry. Remember the quasit's and skeletons' damage reduction. I don't recall if there's anything fishy about the twig blights. If you plan on running them through the Heart of Nightfang Spire, remind them (at the end of tSC) that they can't possibly let such an evil tree remain standing...
