It is impossible to spot reduce when it comes to fat loss. You will have to lose fat everywhere to lose fat on your back.
Diet should be full of primarily lean protein, healthy fats and veggies. Find out what your maintenance calories are and subtract 200-500 calories from that. This is how many calories you should eat.
For fat loss, I suggest a full body heavy lifting routine 3-4 days a week. Incorporate compound lifts like squats, deadlifts, clean and press, rows, dips, chin ups, pull ups, bench- they are all great movements that will work your entire body very well.