Converting a 3.5e Campaign to a 4e Campaign

I've played D&D on and off for a number of years and I thought that it would finally be time to try my hand at DM'ing using Roll20. A little while ago, a friend bought me the Shackled City Adventure Path and I'd like to base my campaign around that. However, what I'd like to do is convert it for use with 4th Edition - possibly even the Neverwinter campaign setting. The drawback, I have absolutely no idea what I should do or where I should start with making it viable as a 4e campaign. I'd really appreciate being pointed in the right direction. Thanks for any help in advance.

The first thing I'd do is look up the monster stat blocks, if they are close to the same you can swamp them out. If they are very different...find something that makes sense to the story to substitute? Another option is creating your own monster, though that takes a lot of thought and prep time. I've stuck with 3.5, but I've known DMs to do a lot of conversion from ad&d and other things.

That sounds like quite the project. Shackled City is pretty huge. I would start by just converting the first adventure before you run it and see if you think that it'd be worth doing the rest. I'm guessing you like the storyline/setting/NPCs of that path and as long as you keep those intact that's the important part right? I have converted one 3.5 adventure to 4e but it was much shorter than an entire adventure path. I was lucky enough that for the most part the monsters in the adventure stayed roughly the same power level, I added or deleted a level here or there. I added some minions to a big fight, just for fun basically. I substituted a couple of creatures with something similar that I found in the 4e book, because there wasn't the exact same thing. Also, I added a skill challenge to it, because there was an area of the adventure where it worked out very well.