Exercise problem! Desperate please help! :)?

Heey, Im 17, 172cm and 76kgs. I obviously need to lose weight but i was wondering what is the right exercise to tone your whole body? I struggle to find time to exercise as im at school and have trouble avoiding the unhealthy foods. I really want to look nice and like my image. How do i get the motivation i need and reach my goal weight? I have tried everything and nothings working for me. I dont have time to join a gym and was thinking of doing a zumba class and buying an exercise bike will that help lose weight? And how much exercise should i do a week to lose a kilo a week or see good results? and what weight should i be - that would help??? Pleasssssse help me, it would be muchly appreciated!! <3 Thanks a million