If you wish to change the name servers for your domain this can only be done by the company that the domain is registered with. If the domain is registered with Claranet SOHO and you wish to change the name servers, this can be done by sending an email to domainchange@uk.clara.net with the request. On this request you will also need to confirm security information and will also need to specify the new name servers.
Please note: If the name servers are changed this will effect where all DNS records for the domain point to so this may also affect the MX records, A records, CNAME records etc.