When you update nameserver for your domain or update DNS record, you might not see immediate change when you browse the website because it might still take you to the old server or IP address. It happens because your changes have not yet been properly taken to all intermediary network it takes for you to reach your website. It is called DNS propagation. When you visit a website, it passes through multiple ISP networks before reaching your website server. Those ISPs have their internal IP caching system that stores the IP address for a previously visited website for a certain period. It can be up to 24 hours. That’s why sometimes it takes up to 24 hours for new DNS changes to be properly propagated.
DNS records are stored as cache in multiple levels. Caching firstly happens on browser, your computer, router, your ISP and all other ISPs in between you and your web server. There are several ways to clear the cache on a browser and local network level. The easiest is to use Google DNS servers as your default DNS servers so that your DNS records are updated quickly. After you have cleared cache from your browser and PC, you can flush google DNS from here (https://developers.google.com/speed/public-dns/cache?hl=uk). You can do this by visiting the link and entering the domain name there and keep the record type A, complete the captcha and click on Flush Cache button.