Your blood sugar level can be lowered by exercising. However there is a counter indication to that. In case your blood sugar level is above 240 mg/dl, you may check your urine for ketones. If you have ketones, you should not exercise. Exercising with ketones is counterproductive, and may make your blood sugar level even higher.
Making changes in your food intake can help as well. Your dietitian can help cutting the amount of food you eat. If exercising and dieting are not enough then your doctor may change your medication or insulin, or even the timing of that.
Work with your doctor to find the safest way for you to lower your blood glucose level.
Hyperglycemia can be prevented with good diabetes management. Another important practice is to learn to detect hyperglycemia early so that you can treat it before it worsen.