For starters, was it just your cholesterol that was high? or did you also have high triglycerides?
Gymcoach is absolutely right, genetics can play a big role, especially if you have a family history of: early heart attacks, heart disease, atherosclerosis etc. That would be a place to start, and then discuss that with your doctor.
In terms of reducing your numbers. The best thing in my oppinion is diet and exercise. I myself have a big family history of high cholesterol and diabetes in my family, and I once had bad numbers as well. But through diet and exercise I changed that. In diet, you are going to want to reduce your fat content, specifically your saturated and trans-fat. This would include: Bacon, sausages, burgers, fries, lots of red meats, butters etc. Start eating healthier meats like: fish and chicken (but not the fried kind
In terms of exercise, start running or biking or do something that will give you a good sweat for 30-40 min. If you are worried that your numbers are high, based on your hight and weight that you gave us: try losing 5-10 lbs. Even that small amount of weight can help WONDERS for your cholesterol numbers.
Finally, there are medications (like Lipitor) that can help with cholesterol problems. But beleive me, you do NOT want to go on medications. It should be one of your last resorts.