Hi Alam EIT,
you mentioned that " study permit will expire on May, 2017 but my study visa will expire on August, 2016". as per your statement it look like initially you have been issued student visa( visa sticker affixed in your passport page) which has expiry date August 2016. on based of it when you enter Canada at the port of entry(airport immigration exit point) CIBC (immigration) officer issued a study permit expiry date same as your sticker in passport as well your proposed study period in Canada.
Meanwhile, somehow your study is not finished till August 2016 so you needed to extend your study permit which was issued to you till May 2017.
so now you asking about extending your visa sticker which is called TRV(temporary residence visa) and it only needed for re-enter Canada. if you do not have any need to travel out of Canada so there is no need to renew it which cost $100. even if you still want to renew it so you can apply by searching in CIC website "Apply for a new temporary resident visa from within Canada"
hope it will help to take right decision.
