In 123-REG

Go to Control Panel Home and log in.

Scroll down to Domain names. Select the correct domain and click Manage.

Scroll down to Advanced domain settings and select Change Nameservers (DNS).

Remove the old nameservers and put:

nameserver 1: ns1.tsohost.co.uk
nameserver 2: ns2.tsohost.co.uk
nameserver 3: ns3.tsohost.co.uk

Then click update.

In Go Daddy

sign in.

Beside domains click Launch.

Select the right domain.

Below nameservers click manage.

At the top it should say custom.

Above right click Edit nameservers.

There will be space for two, put in:
1: ns1.tsohost.co.uk
2: ns2.tsohost.co.uk

Then click OK.

Then click add nameserver. In the box put:
ns3.tsohost.co.uk

Then click OK.

Finally click Save.