Hi, having high blood sugars can suggest underlying diabetes but should be confirmed with a repeat blood test.
It may not entirely be due to an improper diet or lack of exercise, as many cases of type 2 diabetes can run in the family. Depending on whether you are on any other types of long term medications such as steroids, they can also lead to high blood sugar.
The basic management of high blood sugar/diabetes would be regular exercises at least 150 min of moderate intensity exercises weekly, together with a healthy diet comprising of vegetables, proteins and portion controlled carbohydrates, and omitting refined sugars (cookies, candies, soft drinks).
Besides that, if sugar levels are quite high, medications can be started.