You can apply to renew your study permit if you want to study longer. It is important to apply well before your current permit expires to ensure your permit remains valid.
When an applicant approaches port of entry in Canada, the CBSA officer examines his or her travel document/passport, an adhesive sticker, and permits the person to enter Canada. The CBSA officer stamps his or her travel document/passport and hands over a status document named as study permit. This documents entails the duration of his or her study permit. If an applicant wants to extend his or her permit to study in Canada, he or she will have to submit an application for extension of study permit. Generally, a 30-day period is recommended by IRRC before the expiry of the status granted.