So, what to do?
Well, industry standard for ease and accuracy is to measure body fat using calipers. Calipers measure based on how much fat you can "pinch" in your body in various places. Over time, this can give you an accurate result regarding how much fat you are losing or how much muscle you are building. Calipers aren't perfect, though, and the numbers will be most accurate if you are measured by a professional.
Body fat analyzers pass an electrical current through your body. Fat impedes electrical current more than muscle does, so the machine can estimate body fat percentage from how fast the current returns. These can be quite inaccurate, however, for people who are very athletic or people with low body fat. Over time, however, they can let you know if you are losing or gaining body fat or muscle, which is helpful when motivating yourself to continue training! Some analyzers are more sophisticated than others, and can give more accurate results even for athletic muscular individuals.
Many people want to monitor their body fat and muscle percentages in order to gauge how healthy they are or how their training is coming along, and using calipers or a body fat analyzer is a good start!