Updating the domain name nameserver settings on your 123-REG control panel is very straight forwards, but first let me tell you why the nameserver settings need to be updated. The best simile I can think of is to imagine your website is a book and your domain name is a library index card. Amongst other things, the index card has the name of the book (in our case the domain name) and where it is located (in our case a server or computer if you like that is permanently connected to the internet). Search engines (Google et.al.) and Internet Service Providers (ISP’s such as EE & BT) use the library card to find your book; If we move the book, we have to update the library card. Chances are you are reading this because I have taken over the hosting of your website (book) and we need to update the domain name (library card) so as it points to my server.
Anyhow, I think you have enough background, let’s update the settings.