The university has a duty to keep records of international students' passports, visas and ID/biometric cards, as well as their contact details, so you must keep your contact details up to date.
If a student has a Tier 4 visa, the university also has a duty to report to the UK Border Agency (Home Office):
any students who fail to enrol on their course;
any unauthorised absences from the course;
any students who discontinue their studies (including intermitting and deferrals);
any significant changes in a student's circumstances, such as a reduction in the length of the course
if the university stops being the student's sponsor for whatever reason;
any suspicions the university may have and evidence that a student is breaking the conditions of their stay in the UK (e.g. working more than 20 hours per week during term time)
For further details, please:
read the university's information
read further information from the UKBA
If you have a Tier 4 Student visa, and you wish to change to a course at a different university from that stated on the visa letter and your visa application, you must either get permission from the UKBA or make a new immigration application before you can change.
If you made the application for your current Tier 4 visa before 5 October 2009, you must get permission from the UKBA.
Until 20 April 2011 you need to email the UKBA to ask permission to switch.
After 21 April 2011 you must request permission to change institution using the Permission to Switch form and pay a fee of £160. The forms have not been published yet.
If you made the application for your current Tier 4 visa on or after 5 October 2009, you must make a new visa application.