well if you want to lose weight and bulk up then dont start lifting immediantly thinking it will help you lose weight. try doing some cardio workouts like running for 2 miles everyday or jogging. also try to watch what you eat, every morning eat some fruit like an apple or banana before you start your day, for lunch eat a peanut butter sandwich but only put the peanut butter on 1 piece of bread. for evening meals eat a salad with some toppings but for the salad go big on it because its healthy and you dont want to starve. once you get get rid of the fat you dont want then start lifting dumbbells. depending on how much you can lift try lifting 40lbs doing 5 lifts a rep for each arm, I prefer doing 5-8 reps a day. after that then I suggest doing the maxed out weight you lift as many times as you can and then do a 1 mile run. do 20 push-ups and 40 sit-ups each night before you go to bed. continue doing this for about a month or two and I swear to god you will be a tank.
Some of the best exercises to get rid of fat are aerobic exercises and abdominal workouts. Some of these exercises include cardio, weight lifting, and outer leg lifting. You should also eat balanced diet with less fats.
Just keep in mind that because muscle weighs more than fat, you will probably initially put on weight at the start. To burn off fat there is no better exercise than running/jogging. The excess weight & fat will rapidly come off & improve your muscle tone.
Also see your doctor before undergoing any new exercise regime.
To keep an I on your progress, keep calculating your BMI body mass index. You can calculate this by dividing your height by your weight which gives you a % of body fat. There are other ways to calculate it. Just google it.