If your web hosting in the same server …
Just copy the files to for example mysite.com/blog to mysite.com using ftp …
Just move files from the hosting to your computer than upload it again (using ftp like filezilla) …
after that edit wp-login.php in your mysite.com
add this in that file :
update_option(‘siteurl’, ‘https://mysite.com’ );
update_option(‘home’, ‘https://mysite.com’ );
Note :
if you have many manual links which point to your old domain. Just using plugin to replace the old links (https://www.ads-software.com/extend/plugins/search-and-replace/)…
