lowering BF is all about calories in vs Calories out im afraid, what that means is you have to burn more than you consume. there shouldn't be a hectic deficit, just a small one. its usually by trial and error where you weigh yourself and adjust your calories over time. you can use this calculator to measure what your calories need to be and then just slowly adjust from there. (gaining weight eat less, losing weight slowly perfect) if youre gymming and a beginner you should put on muscle anyway as long as your having adequate protein in your daily meals. anyway hope that helps a tiny bit