Diet alone wont help much but exercise is equally important along with diet. he has to avoid ghee, butter, cream, egg yolks, red meat (avoid all meat for few months). also avoiding all fast foods, ice creams. Also avoid all nuts/oilseeds for few months then it can be taken in moderation ... 8-10 cashews/almonds/ 2-4 wallnuts, little groudnuts...go for almost boiled foods. maximum 2-3 teaspoons of oil in a day and that's too olive oil or sunflower oil or soybean oil. eat more fresh fruits and vegetables, sprouts, whole wheat flour, vegetable salad only dressed with lemon. He has to develop healthy dietary habits. If possible seek a help from any dietitian. Also keep starchy foods, sugars, any sweets in control. Can use lemon freely, it will improve the taste of the food.
Its also depend if he has any family history. Might be some drug will be prescribed by the doctor to lower the cholesterol
level. If he has a family history then he has to be more careful after things come under control so healthy dietary habits is of immense help to keep things under control along with few life style changes which is not very difficult.
Remember exercise is equally important so its better to seek doctors help in this regard as he will only guide you regarding exercise. never to over stress
while doing any exercise. He can go for a brisk walk ( start slowly... start with 1 kilo meter continued for 4-5 days so he will get use to it gradually increasing distance and the speed too slowly) 4-5 kms is enough for him which takes 40-45 mins. Or else he can go for cardiac exercise in a gym but there should be a trained personal trainer to guide you. So make enquiries whether he is properly trained or no?
Also check whether triglycerides is in normal range or no as it is also a risk factor along with cholesterol level. It is also a type of cholesterol.
Good luck !!!