Carbs and calories are a challenging thing to master ....so much depends on how much you burn and how you burn.
It is correct that too much carbs will convert to sugar then fat...none of us want that.
However...what you should concentrate on is the type of carbs and the "net" carbs.
Net carbs are the total amount of carbs minus the total fibre. We don't absorb fibre so it can be subtracted from the amount of carbs to get your net count..this is the number you should be concerned with when calculating. It's always better to consume the more complex carbs....dark green veggies and beans...and avoid white foods and sugar.
If you want to lower fat percentage and increase muscle mass(tone up) or just lose weight...you can start by cutting your current calorie intake by 500 a day..(provided you are over the 1500(+/-) mark..if you have already done that and still not losing weight..or getting results. It's time to cut back the carbs...check to see how much you currently take in in a day...An active healthy adult who works out 5-6 times a week should consumer approx. 150-250 grams a day..
For me....after having 2 kids my metabolism was so slow that going over 100 grams a day even with exercise increased my weight. I had to start low...cut back on carbs severely then gradually add them back after I started losing weight...once I reached a point where I met my goal weight and wasn't losing anymore...I recorded the number of carbs I took in a day and no longer exceeded that. I should mention that I was 5'4" and 185 lbs getting started after baby #2...and managed to get down to 130 lbs before getting pregnant with baby #3 and like before ballooned up, I was 192lbs the day I gave birth.
That was 7 months ago....I followed the reduced carb plan and now sitting at 153lbs and steadily going down.
As for calories, it's really difficult to know how much you actually burn a day...you would have to get a test done, if you wanted to know specifically..Guidelines suggest a woman should not go below 1000 calories a day...below that your body will go into starvation mode.
We all require carbs, proteins and fat...if you choose..lean, non trans fats, complex high fiber carbs and lean proteins...delete sugar and empty calories..it WILL work.
Exercise and lots of water are keys to making the change in eating habits work, they are all part of the puzzle..one make work but only for so long..you need all parts for success....