You probably don`t even need to cut that drastically at first to lose weight. You may want to cut a bit by looking at/reducing in-between-meals snacking and calories in beverages. You may then want to improve your three meals a day and then, as you get lighter and fitter, slowly incorporate excercise.
If you are a "beginner" and feel your diet is poor to start with, doing it in stages may be less daunting and easier to achieve.
What I can recommend is a food diary, on paper or online, e.g.
www.fitday.com, which is an excellent program which logs your calorie and nutrient intake.
Stella