The duration of your stay depends on the length of your course and what study you have completed in the UK.
If you are 18 or above and studying a degree level course then you can stay up to 5 years in the UK.
If you are pursuing a course below the degree level then you are allowed to stay for up to 2 years in the UK.
If you wish to continue your studies in the UK then you are eligible to extend the visa.