It's a good idea to include oatmeal in your diet, you want to up dietary fibre wherever you can.
Whole grains, beans, lentils, vegetables, such as Brussel sprouts, broccoli, kale, spinach, carrots are especially good.
You could vary the apple in your oatmeal by throwing in some frozen fruits like raspberries and blueberries.
Definitely cut down on high fat dairy, red meat, fried foods, processed snacks.
Don't smoke; cut back on alcohol.
Excess alcohol can increase total cholesterol levels.
Exercise and maintain a healthy weight.
Sub butter with olive oil, sunflower oils.
Good luck OP, it's not hard once you make changes to your dietary and lifestyle.