Just a small loss in body weight will generally decrease PCOS symptoms considerably.
If you're looking for information on PCOS and how to reduce and reverse its symptoms, "A Patient's Guide to PCOS: Understanding and Reversing Polycystic Ovary Syndrome," by Walter Futterweit is perfect. It explains the problems associated with PCOS (excess male hormones, insulin resistance, etc.) and how to reduce those problems in order to have more control over the disease.
With respect to diet, the book discusses insulin resistance and explains the benefits of a Low Glycemic Index diet. Essentially, foods with a higher glycemic index (pasta, rice, potatoes) cause higher spikes in blood sugar after eating them. Rapid fluctuations in blood sugar also increase insulin levels, which can lead to hormone imbalances and weight gain (two major contributors to PCOS). Thus, eating lower GI foods usually helps curb PCOS symptoms; including weight gain/ trouble losing weight, hair loss/ hair growth, adult acne, depression/anxiety, and infertility.
There are also many good and healthy Low-GI recipes in the book. Although a lot of the recipes are not vegan, they can be converted by substituting veggie burgers or other vegan proteins such as tofu or beans for the meat and fish. I also recommend that when you do decide to eat a High-GI food, such as pasta, make sure to pile on the veggies. This will help slow the spike in blood sugar. Whole wheat foods cause slower rises in blood sugar as well, so try to always opt for whole wheat pasta or bread.
This book also contains other important information concerning treatment, diagnosis, and prevention. If you have PCOS, I highly recommend that you read it.