It's really about counting calories and what you eat. Just write down all the things you eat each day for a week. Go online and find the calorie contents of each item. This will give you a general idea of what you need to change. Try to shoot for a 2k calorie diet at first unless you're way up their (like already eating 3-4k) then try 2500. If you eat the right things it's hard to get 3000 in a day without feeling like you're stuffing yourself. If you work a job that requires lots of physical labor then you may need a bit more.