It is the responsibility of the international student to maintain his/her I-20. Every international student should have his I-20 in current state at all times when in the U.S. or on an F-1 visa. The usual course end date would always be for the timeline of your course. But if you change the course curriculum or add few extra courses, the end date on I-20 will be before your graduation date. Hence, you always need to keep an eye on the I-20 expiration date.
For the extension of the I-20, you need to fill an I-20 extension form which is available in the International Services Office. Along with that form, you need to submit a financial document which would cover your tuition fee and living cost in the U.S. The financial document must not be older than six months. Once you submit these two documents, your new extended I-20 will be issued in 2-3 days.