If you want to lose FAT versus weight, start strength training (lifting weights). No, it will not make you bulky like a professional bodybuilder unless you take steroids, but it will increase your lean body mass which is what burns extra calories all day and all night. Are you in your target heart zone with your walking? If so, I'd just keep walking. However, most people do not walk fast enough. Check your heart rate and see. You can always alternate walking and jogging.

Jen