How to change the name servers of my domain?
As long as your domain is registered through SiteGround there will be no problem to change its name servers.
This can be done from Client Area > Services > Domains > Manage.
Click on Manage nameserver and modify the NS records for your domain and then click Confirm to save the changes. It will take several hours for the DNS change to propagate.
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) would 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 in the DNS zone of your new provider in order to ensure minimal downtime and/or propagation.