I would suggest finding a website that lets you track diet and exercise. Many, like Fitnespal and FatSecret are good for tracking diet, but generally overstate your basic daily caloric intake requirements, and the amount of calories you burn working out. I use Training Peaks now for about a month. It does a better job than any other I have found. Determine the amount of calories you burn just by waking up and breathing. For your size I would guess that's about 2000.

The best way to figure the calories burnt riding is with a HRM, and using a tracking app like Strava or Endomondo. I use Strava, which I download ride data from a Garmin GPS. You can use a smartphone too.

Add your workout to your daily base calories then aim to eat 200-400 calories less than that.

As far as carbs go, I checked out this whole Atkins thing and found that my initial assumptions about it were inaccurate. Carbs are not bad, and Atkins does not really say they are. The reality is that in the last 60-70 years the amount of carbohydrate in the typical American diet has increased drastically, mostly due to the increased use of a new, inexpensive, flavor enhancer called high fructose corn syrup. In a word - sugar. They put it in dang near everything.

If you are working out pretty intensely, you can tolerate, and actually need more sugar. You can look up carboloading elsewhere, as it is more involved than cramming down pasta and cookies. Those websites mentioned above will give you a breakdown of the macro nutrients, fat, carbohydrate and protean. You can go by grams, or by percentage of total calories, which I prefer. I am currently getting about 20-25% protean, 30-35% fat and 35-40% carb. This is what works for me. everyone is different, but not drastically. I have health issues (cholesterol) that dictate that almost all of the fat comes from nuts, omega3 oils, and lean meats like chicken and fish. The carbs come mostly from whole grains, lots of vegetables, including beans, and on days that I ride hard boosted with sugar from honey, clif bars and sports drinks.

You will get a lot of different advice here. Read all of it, experiment, but be dubious of anything that sounds really wacky (my brother in law is now doing a regimen that involves eating all the junk he wants but as long as he doesn't eat between 7:00 pm and 11:00 am, he's golden. I put on a dumb smile, nod and say "oh really? That's nice" )