I switched from CD to Atkins a couple of years ago. The switch is quite easy food-wise but you need to eat a lot less carbs on Atkins. Induction - the first phase of Atkins - permits only 20g of carbs per day, of which 15g should be from (preferably) green leafy veg. Cauliflower, broccoli, cabbaget etc and salad veg (not carrots or onions to begin with) are ideal.
The rest should be protein and fat. Don't skimp on fats, they are essential on Atkins.
Check the sticky above and also check The Atkins Community site for tutorials and advice and lots of interesting forum chats.
Good luck!