Firstly you should read the advice on extending your visa here: Tier 4 Guidance Notes.
Secondly you need to complete a Confirmation of Acceptance for Study (CAS) Request Form.
It is very important that you prepare the supporting documents for your CAS Request Form in good time; it will not be possible to issue you with a CAS until you have provided all the correct supporting documents with your CAS Request Form.
Some students are not able to extend their visa in the UK; if you are advised that you cannot extend your visa in the UK you will not be issued with a new CAS until you have provided a scanned copy of your boarding card for your flight home to The Student Immigration and Compliance Team (SICT) SICTSupport@uclan.ac.uk.
Standard Tier 4 visa applications make take several weeks to be processed by the Home Office; the average time is 8 weeks, but it may take longer. You should not make any plans to travel outside the UK if you need to make a standard Tier 4 visa extension.
The University cannot speed up your visa application with the Home Office. If you prefer, you may wish to use one of the Home Office’s faster services – either Priority or Premium: www.gov.uk/tier-4-general-visa/extend-your-visa. Please note that both these faster services cost considerably more than the standard service. For further information on the Premium Service: www.gov.uk/ukvi-premium-service-centres/overview.
This leaflet explains what a biometric residence permit (BRP) is, what it can be used for, and how employers can check that prospective employees have a right to work in the United Kingdom.