Unless it is due to the death of the account holder you can't.
You would need to cancel the account and start a new account.
Welcome to this user forum for BT Retail phone and broadband customers.
You cannot change the name of the account holder.
The existing account holder would have to cancel their contract, and a new contract would have to be started by the new account holder.
This could result in cancellation charges and a loss of the phone number.