On the day appointed, the county commissioners shall meet, examine the premises described in the petition and hear the parties present, and thereupon they shall determine whether said ways shall be raised and the water vents enlarged and to what extent, and shall prescribe the manner in which it shall be done, and what portion of the expenses thereof and the costs of the hearing shall be borne by the petitioners, and what portion, if any, by the town where the way is located.