Cholesterol. Cholesterol accumulation?

Hi all, Since it's work from home my job requires me to sit in the system for 9-10 hours as I'm an IT engineer but I've been very much cautious about my health so I hit gym regularly and go for brisk walking with cardio exercises.for past 3 months In the craze of Fitness and to fulfill my protein need I was feeding on cow milk which I believe it to be fatty ever since then I feel my body is becoming inactive as I feel tiredness, drowsiness, fatigue and for smaller activity I would feel tired and exhausted as my heart rate would increase at higher rate. I strongly believe my cholesterol is the major reason for this. As of now I've changed my diet and it's completely dairy free. I see gradual improvement in all the activities. Could you please tell me how one can reduce cholesterol and symptoms of high cholesterol? Were my above symptoms are indications of cholesterol accumulation?