WordPress
Move a WordPress site without a long outage
A careful move copies files and the database, then changes DNS only after the copy answers. Mail should move in the same window if you can.
Copy files and export the database before you touch DNS. Import them on the new account, set the table prefix, and fix the site URL in the database if you are also changing the domain. Browse the copy with a hosts-file override so you can see it before the world does.
Then lower the TTL at the old DNS, wait, and switch nameservers. Mail moves only if MX, SPF and the mailbox contents move too. Leaving MX behind while changing the website is a common way to lose a day of enquiries.
Take a downloadable backup on both sides the same day. A copy that exists only on the server you are leaving is not a copy you can reach after the password changes.