Michael on "Child Theme"

if you want to use a child theme for your own site?

FTP https://codex.wordpress.org/FTP_Clients

https://codex.wordpress.org/Using_Themes#Adding_New_Themes_Manually_.28FTP.29

if you have developed a theme for the theme directory:

https://wordpress.org/support/topic/add-your-theme-to-the-wordpress-theme-directory?replies=1