Hi Kathy,
For total body Cathe workouts, I would first recommend Drill Max, High Step Challenge, and Boot Camp. All of these include cardio with the weight training, which I've found helps lean me out far better and more quickly than splitting my weights and cardio into separate days.
As far as increasing the weight of the dumbbells you are using, I would say go ahead. 12.5 is pretty light, so I don't think that weight is causing you to bulk up. There is a fine line between lifting heavy enough to tax your muscles and start the fat burning process, and lifting too heavy and becoming too bulky. Also, it depends on which body parts you're working and the exercises as to how heavy you want to go. For me, I've found that moderate weights, 12-15 reps, and incorporating plyometrics has made a huge difference in my lower body.
One final thought, 80% of what your body looks like is due to what and how much you eat. For stubborn fat loss, you will have to eat ultra clean and be aware of everything you put in your mouth. I honestly don't believe that our age prevents us from losing weight. I'm 47, and my body looks better than it every has. I didn't even start worrying about it until I was about 43, so trust me - it's not your age!!