Siteground - How to change Name Servers?
As long as your domain is registered through SiteGround, there will be no problem changing its name servers.
This can be done from Client Area > Services > Domains > Settings.

Open the Name Servers tab and click on Manage.

In the pop-up window, choose one of the available options in Nameserver Type.
- SiteGround – Choose this option if you want to manage your DNS records with SiteGround.
- Private – Choose this if you wish to use your own private nameservers as an alias of SiteGround nameservers. Suitable for white-label hosting where you want to manage the DNS records through SiteGround.
- Custom – Choose this option if you want to manage your domain through third-party nameservers. You can type the nameserver hostnames in the Nameservers fields.
Once ready, press the Confirm button.

If you are not a SiteGround customer, you should be able to edit your name servers from the control panel at your host/domain Registrar. For more information on how to do this, you will have to contact your host/Registrar.
IMPORTANT! When you change the name servers of a domain, all advanced records (A-records, CNAME-records, MX-records, SRV-records, and so on) will resolve from the DNS zone of the provider whose nameservers you are setting. Thus, if you are using a custom A-record or MX-record for your needs, it is strongly recommended to add them to the DNS zone of your new provider before switching the nameservers. This ensures minimal downtime and/or propagation.