Create a 500-1000 calorie deficit. Some people create a harsher deficit, and rely solely on diet which will still work, but the lethargy affects your ability to train hard.
There are many cardio haters, but I am sorry, HIIT coupled with resistance training will get you there. Hormones like leptin are affected by severe caloric deficits, so it's a good idea to have a carb up day if you're really cutting hard.
To be honest, and as cliche as it is, it really needs to be a lifestyle change. I'd cut calories harsh for a maximum of 2 weeks, then taper into a 500 calorie deficit and go steady, incorporating ~3-4 days of resistance, and 3-4 days of HIIT.