You could also plan to complete the migration during your site’s low-time – try to identify when there are the least visitors on your site, and migrate at that time.
Select a username and password that you’ll use when entering the details at the new host.
Ensure the hostname box is filled out correctly – usually it auto-fills that box with the correct information, but if not, then have a look around the host site and see if they have a blog/article that states what the details should be. You may have to contact their support system and ask.
Lastly, select the domain that you wish to migrate, and ensure that it is filled out correctly in the corresponding box. You can use FileZilla to help setup and connect to the FTP accounts you need, or use it as a diagnostic tool to identify where the problem with those details are.