Below you will find the steps needed to change the DNS Nameservers for domains registered with 123Reg.
1) Login to your 123Reg account
2) In the Domain Names section, select the domain you wish to modify from the dropdown menu, then click manage.
3) Select Change Nameservers
4) Enter the nameservers you wish to use
5) Click the Change Nameservers button
Note: Your domain must be unlocked before changing the nameservers. You can unlock your domain by clicking the Manage Domain Locking option, then clicking the Unlock Domain link.