Like I said in my article here (http://goguda.hubpages.com/hub/Is-Cholesterol-Real... you should not worry about lowering cholesterol, as it does not cause heart disease. In fact, low cholesterol is a lot worse for you than high cholesterol.
Exercise will not prevent heart disease, but can definitely strengthen your heart and make it function better. You should probably get about an hour of physical activity per day minimum.
As for cholesterol, like I already said, there is no reason to lower it. Although, to raise your HDL (Lipoprotein that carries cholesterol back to the liver, most often called "good cholesterol"), you can try incorporating more fat into your diet. The only thing that increases HDL is fat in the diet, especially saturated animal fat such as butter, red meat etc. Contrary to what you have been told, saturated fat will NOT clog your arteries and is actually crucial to proper health. Increasing your HDL will just make your cholesterol system function more efficiently.
To prevent heart disease, limit your carbohydrates such as bread and refined sugar (especially high fructose corn syrup), but eat as many fruits and vegetables as you want. This will prevent inflammation by keeping your blood sugar low. Of course, if you do decide to reduce, or dare I say, eliminate bread and refined sugar in your diet, you need to make up for the loss of calories with fat and protein.
This definitely will probably sound strange to you, but this is how our ancestors ate, and heart disease was EXTREMELY rare back then. Heart disease rose when people started cutting back animal fats such as butter (from 18 pounds per person per year to 4) and the consumption of bread and sugar increased. So, as long as you keep your sugar intake low, having more fat in your diet won't do ANY harm, and will actually benefit you.
Also, don't be scared to eat cholesterol. Studies show that the more cholesterol people eat, the less cholesterol in the blood. This is probably because the body doesn't have to make it's own cholesterol.
So in short, don't worry about your cholesterol levels; there is no need as cholesterol is not the cause of heart disease. To prevent inflammation, cut out as much bread and refined sugars as possible, and limit vegetable fat (margarine, vegetable oil, etc.) use.