Im trying to lose weight. Need a plan, help please ?

I've began trying to lose weight. I'm 17 years old & weigh 240lbs. My diet plan consists of eating a bowl of Raisin Bran for breakfast at 10am. Then I eat a Turkey sandwich at 3:30pm. Then i go to the gym & get on the treadmills and speedwalk at 4mph for around 2 hrs. then i come home & eat 2 sandwiches at 8pm. Is this a good plan ? or is there a bette rone ? thanks for the help