How do I start eating healthier after a life full of junk?

As far as I know I've been eating junk food all my life. I'm now 15 and It's getting to a point where I know I need to change my eating habits. I don't look fat on the outside but I know I'm doing lots of damage to my insides. I'm a pretty lazy person but I do play tennis twice a week and I see food as an easy treat which doesn't require any effort, lately I have been having an apple as they don't require much effort but I know this isn't enough to help reverse the damage of 15 years of junk. A days worth of food will consist of maybe rice bubbles or ice-cream for breakfast, at recess at school I might have 4-5 biscuits a pack of chips and maybe an LCM. For lunch (if i have any food left) a couple of biscuits and after school i may have some more biscuits and some lollies and a fizzy drink. It's also hard for me to eat healthy because I don't like lots of veggies (mainly the green ones and lots of other ones) but i do like some fruits. I'm afraid that i will get diabetes and possible have heart problems which i really don't want because one night my heart felt really bad and almost felt like it stopped and it really hurt and I don't want it to happen again. Please give me some advise on what i can do to start eating healthier and reverse some of the effects that have been cause by my bad habits .Please help me before its to late.