Hi there!
As suggested by ‘gymdandee’, diet modification can be an effective method to increase your metabolism. Diet modification should be aimed at taking adequate calories are required for the mount of physical work, however slightly decreasing the carbohydrate intake and increasing the protein intake with plenty of fruits and vegetables. You could also start exercising the upper body like weight lifts etc.
Hope this helps.
Take care!
protein powers up your metabolism like no other nutrient source!