If the diet you consume now is "crappy"- too much animal protein, dairy, fats, refined sugars/flours, and overcooked/canned veggies, and you make a fully educated transition to a vegetarian diet that is balanced with enough calories, you will almost certainly lose weight as a result of eating a clean healthy diet--this holds even more true with a proper vegan diet.
DO NOT think that vegetarian/vegan"ism" is an instant panacea for weight loss- although incorporating it into being a lifelong habit offers amazing benefits to your long-run health and will help your body maintain your "natural" weight.
When I first became a vegetarian I did it for my health, having studied nutrition for years it still took me about 18 months to make a full transition away from meat and other "unhealthy" (

) eating habits I had. I'm now vegan for many other reasons as well.
I do not eat ANY processed foods. I eat a lot of fruit, especially early on in the day, and most of my raw veggies I juice or pulverize in the Vita-mix, this makes undigestible fibers much easier on the digestive tract, not to mention my jaws. I consume a lot of whole grains- cereal grains can be cooked just like rice. Also beans, nuts/seeds, legumes, and soybean products. I love to cook, and I enjoy knowing my body is healthy because of the nutritious foods I put into it. If I season, I use only herbs and spices, sea salt, if ever used. The only oil I heat is extra-virgin olive, I eat this every day along flax oil and an avocado.
Making the switch is not easy, especially if you are cooking for other poeple. If you are able to try it for a week, then do so to see how you feel, it certainly won't hurt you

. Starting out it makes it easier if you plan in advance what you are going to eat for a whole day. Ther is a lot of good info on the WWW also. Regards.