Any DNS changes you make (nameserver changes, or changes within DNS zones) are subject to propagation.
Propagation is effectively the time it takes for parties other than ourselves to pick up on the DNS changes you've made. They "remember" (or cache) the previous DNS record, so need to be given time to "forget" (or refresh their DNS cache) before the changes are seen from a public perspective.
There are 3 components that cache DNS and are therefore subject to propagation:
- Your computer
- Your router
- Your Internet Service Provider
You can try clearing your computer's and router's DNS cache to speed up the propagation from your perspective.
If you're using a windows based system running this command at the command line:
ipconfig/ flushdns
If you're using a mac you can flush it's DNS cache by running this command in the terminal:
sudo killall -HUP mDNSResponder
Most routers will clear their DNS cache if you reboot them.
Should the above not have the desired effect, then your ISP caching DNS records. As this cache can't be forcibly refreshed, it would be a case of waiting for your ISP's DNS cache to naturally refresh.
You may be able to work around your ISP’s DNS caching by setting google’s DNS server’s (8.8.8.8 and 8.8.4.4 for IPv4 and 2001:4860:4860::8888 and 2001:4860:4860::8844 for IPv6) to be used by your computer’s network adapter. How you’d do this varies between operating systems and versions.
