Would this help me lose weight?

normally i just have fruits for snacks vegetables and salad for lunch meats and/or vegetables for tea. oh and a healthy cereal for breakfast. Can i swap my recess for weightwatchers bar, and swap my breakfast with slimfast shake. Then when i get home from school i would have fruit and normal tea. Would this help me lose weight? I have a pretty active lifestyle. My normal healthy eating habits aren't working. Thanks :) x