It's not "hard" but there are a few tips that you need to know and to try and diagnose your carb over the internet would be a guessing game. Go on eBay and pick up a copy of "Rochester Carburetors" by Doug Roe. I've seen nice used copies for under $10. He was one of the GM engineers that helped design it. It has everything you need to do a good rebuild or performance mods. I bought mine 25 years ago and I don't let it out of my sight.
Another good one is "Rochester Quadrajet Carburetors" By Cliff Ruggles. It's much newer and I haven't seen it that cheap, usually around $20 plus shipping. I just got a copy and haven't had a chance to really get into. So far I prefer Doug Roe's by a slight margin but it hasn't been updated since 1987 and the Ruggles book has some newer info. If you can I recommend having both.