HMPO覆我都係話 : passports and documents are dispatched separately and may not be delivered on the same day
https://www.gov.uk/transfer-visa Your name or personal details have changed
You must replace your visa with a biometric residence permit if your overall stay in the UK is longer than 6 months and any of these details change:
date of birth
You do not need to get a biometric residence permit or report any changes if your stay in the UK is less than 6 months.