There's no definite rule about how many times to feed since it really depends on your individual cat: their weight, health, activity level.
Many adult cats do fine with 2 meals per day, morning and evening. My own cats are fed 3 times per day because my oldest kitty needs that many meals due to health issues. She requires more food because she burns up calories quickly - but I'd never get away with feeding her 3 times and my other little guys only twice, so the other two get a "snack", (a small meal) and that way no one feels left out! I don't think free feeding (leaving dry food out at all times) is a good idea - I feed dry food as a treat only, never a meal.
When you're trying to get your cat to lose weight, try sticking to a normal feeding routine (if you had one!), just feed a smaller portion. Leaving food available (even "low cal" food) all day defeats the purpose. If you've done that in the past, try leaving out less than usual, gradually cutting down the amount til your cat is used to eating at designated meal times. What works for people works for cats: less calories, more exercise!