老豆話個時要簡bno定特衰,佢幫我地全家換哂特衰 - you cannot renounce your British nationality in such a manner. You will need to make a formal application to the Home Office in the UK in order to renounce your British National (Overseas) status.
Another point to note is that no one can renounce a child's British nationality on behalf of the child. The Home Office will not allow anyone under the age of 18 to give up his British nationality.