1) Add alternate name
> netdom computername /add:<NewAltDNSName>
Specifies to create a new alternate name. You must specify a fully qualified domain name, which is the computer name followed by the primary Domain Name System (DNS) suffix, such as comp1.example.com.

2) Make new name primary
> netdom computername /makeprimary:<ComputerDNSName>
Specifies to make an existing alternate name into the primary name. You must specify a fully qualified domain name, which is the computer name followed by the primary DNS suffix, such as comp1.example.com.

3) Reboot
> shutdown /r /t 0

4) Verify new name
Check in the System properties.

5) Remove the old name
> netdom computername /remove:<AltDNSName>
Specifies to delete an existing alternate name. You must specify fully qualified domain name, which is the computer name followed by the primary DNS suffix, such as comp1.example.com.

6) Final check
> dcdiag