It is to change the domain management company.
After the domain has been transferred to another company, the DNS records will stay the same.
To switch a server/web hosting, you must change the nameservers, or point your DNS to the new server when the new server is ready.
To add DNS records for domain in Z.com: https://my.web.z.com/index.php?rp=/knowledgebase/47/Where-do-I-edit-my-domain-DNS.html
To change nameservers in Z.com: https://my.web.z.com/index.php?rp=/knowledgebase/46/How-do-I-edit-my-nameservers.html