What is the IPS TAG and what is the DNS - Domain Name Server?
Several features can be controlled for a domain name, such as the IPS TAG and the DNS.
The IPS TAG determines the company you registered your domain name with. I.e. the company you pay money to for buying/renewing your domain name (such as www.123-reg.co.uk).
If you want to change the IPS TAG because you would like a different company to "look after your domain names" (for price reasons for example), you need to contact the company you registered the domain with and ask them to change the TAG to the TAG of your new provider. Some companies will charge a small fee for this change and are reluctant to "let you go" and want reasons for the change. The company you change your domain name to will provide you with their IPS TAG which you need to hand over to the current company, so that they can make the change. The new company might charge a small fee too for transferring a domain name to their business.
The Domain Name Servers (DNS) (usually two) determine to which web hosting company the domain name points. If you have a domain name with www.123-reg.co.uk, and your webhosting is with www.plugsocket.com (for example), the domain name servers would have to be changed to ns1.plugsocket.com and ns2.plugsocket.com. Your domain name needs to "know" where your website files are. By pointing the DNS to the servers of Plugsocket, your website will be displayed.
Some companies provide you with an extensive control panel that allows you to make changes to the Domain Name servers yourself - as often as required - and without any extra fee.