I was in similar shape as you last summer. I had an elk hunt coming up and had to get in shape for it. I started by getting my diet in order. I cut out the junk and snacks. I stopped having seconds and thirds at dinner. I also started riding my bike. At first I was going on a 4-5 mile ride that would take about 20-25 minutes to complete and I would be out of breath and my legs would burn. It would take several minutes for my breathing to get back to normal. I would ride every morning before work. As I felt better I would lengthen my ride. Eventually I was riding 10-12 miles everyday during the week and then 20 on Saturday. The 12 mile rides were completed in about 40 minutes. As I started feeling better I would pay closer attention to my cadence while riding. By the time my hunt rolled around I had lost about 35 pounds. I have kept about half of it off and am now getting started back.
Good luck