okay, so the first step is to just take it slowly!
you can't cut everything out immediately because that increases your chances of not changing.
so slowly get into a rhythm of walking in the morning and then start in the afternoon as well,
don't cut out all junk food, because it will be hard, but when you are craving, the best thing is to have a piece of food or something like a carrot, also, increase you water intake as much as you can, because keeping hydrated will stop you feeling as hungry.
drinking two glasses of cold water in the morning will speed up your metabolism, making you feel less hungry also!
another thing to help you can be rewarding yourself by buying yourself things such as new clothes and shoes etc. if you buy a pair of jeans or something that you would like to fit in, use them as motivation, so that you can imagine yourself wearing them and feeling good about yourself!
losing weight isn't all about exercise, it's mainly about the food you consume, so don't ruin it by craving or binging.