Just reform your diet. And I have no idea what your workouts look like, but structure them towards your goal. I.e., you want to lose fat-so do high intensity lifts, as well as cardio. Also, if you dont want to lose much muscle, try HIT (high intensity) cardio. Wind sprints, hills on the bike, jump rope, etc. These shock your body, as well as stress those precious fast twich fibers that you want to hold on to.
And as far as diet.....you havent even told us what it is, so hard to help you in that regard. Posting that up would be helpful. Or just do some reading on your own and come back with an informed question, whichever.