Grab a 4e monsters manual and find similar creatures of appropriate level, replace them. Traps and other dangers will be more work since AD&D didn't use much in the way of skill checks and traps tend to just hit you and call it a day. Check out some 4e adventures and the DMG (the best DMG for any edition, says guy who never played 4e) for ideas on how to fill in the stats on things that aren't monsters.