I'm 5'9" and I weighed 290 in August of 2010. That gave me a BMI that's slightly higher than yours. I've lost about 70lb so far and I plan to lose another 40-50. Not half my former size, but pretty darn close. I did not have surgery. I'm 33 years old and never lost any real weight prior to this instance -- in fact, I was pretty hopeless that my situation would ever change.
What worked for me? I completely changed the way I eat with a focus on being healthy. I eat healthy foods in reasonable portions and at reasonable times. I eat 3 full meals and 2-3 snacks instead of constantly grazing throughout the day. I stopped drinking soda and eating fast food (those are the only two things that I absolutely don't allow now and really I don't even crave them anymore.) I log and calorie count all my food. It was time-consuming at first, but now seems like second nature. One sorta "cheat" I did have: I ordered frozen food for the first 8 months of my loss. I used a complany called BistroMD, but there are others. For me, it took away the difficulty of deciding what to eat and how to make it. It taught me portion control and refined what I expected food to taste like. It also convinced me that it's worth seeking out really nutritious food like veggies and lean protein because they are so much more filling. I get more bang for my buck that way!
For me, it was an all or nothing sort of approach (not that I haven't slipped up here and there). My mind-set is that this is a completely new way of life -- it's not a diet. It's how I'm going to eat the rest of my life -- healthy!
So, I guess my (lengthy) point is... yes, it can totally be done. You're here getting info and feedback, which is a great first step. There are lots of supportive chickies around here to help! If I were you, I'd start by logging everything you eat. Get a food scale and weigh out correct portions. And drink LOTS of water. Best of luck!!!