No, unfortunately Tier 4 visas cannot be extended for the purpose of attending graduation ceremonies.  You will need to return to your home country and apply for a Standard Visitor Visa in order to return to the UK and attend your graduation.

You will need to let Registry (studentrecords@yorksj.ac.uk) know that you intend to travel for graduation and they can issue you with a letter inviting you to attend.  You and any family members who wish to attend graduation can use this letter to apply for a Standard Visitor Visa.