Thyroid + gall bladd. Healthy gallbladder and liver uses cholesterol to make bile so normalizing then will normalize cholesterol. Cholesterol is formed in liver under influence of thyroid. Cholesterol is needed to make hormones in body if hormones are unbalanced (high estrogen states) stresses thyroid which slows down increasing cholesterol and if gallbladder does not work and thin bile liver backs so cholesterl high.
Lot's of ways. A diet low in calories and low in fat. Getting regular aerobic type exercise, losing weight if you're over weight and if your levels are significantly high talk to a doctor about getting it down with medication which can lower your risk of heart attack and stroke.