It is essential to keep the records at the domain registry up-to-date with any changes as they happen.
Failure to maintain correct contact information can lead to the domain being disabled or even deleted and made available again for 1st-come-1st-served registration by another person.
Updates to the registrant name on a .co.uk / .me.uk /.org.uk / .ltd.uk / .plc.uk domain name (as shown on a WHOIS at www.nic.uk) can only be made by the .UK registry Nominet, and is treated as a change of ownership, for which they make a charge.
The fee varies based on the changes being made, whether any manual verification is needed, and the type of changes being requested. The normal fee is currently £10+vat for ownership changes performed by the current registrant and £35+vat for ownership changes made by 3rd parties (inc. Nominet staff).
To pay the lowest fee, the registrant will have to make the changes online through the Nominet Registrants-Online Service – you will need to know your domain name (obviously) and your Nominet login details (which they sent you at time of registration). If you do not know the login details, there is a recover/reminder option on the login page.
If the registrant cannot complete this process, then there is an extended proof-of-ownership and proof-of-identity process which must be followed and additional fees to pay.
If the domain is a .ltd.uk or .plc.uk there are restrictions as each LTD or PLC company is only entitled to one domain and it *MUST* match the full name of the company (as registered at companies house) or a verifiably in-use (or trademarked) abbreviation of the name – if your LTD or PLC has changed names, you will need to register a new domain, and not renew the current one.
Current domain registration terms can be seen at Terms & Conditions.