Download to your desktop and install from Appearance > Themes > Add New: Upload Theme.
Activating a child theme will cause menu location and Customizer settings to reset. This is expected.
If you’re using Ultra Premium and have used a lot of the Customizer settings then this, unfortunately, a bit of work.
Once activated go to Appearance > Editor > functions.php and locate:
Insert new alt tag text here
Replace that string with your new alt text. This is an intermediate task. Even the smallest mistake in functions.php can cause your site to white screen. In that event, login to your server via FTP and delete the Ultra child folder at /wp-content/themes/ it’s called “ultra-child”.
If you’re already using a child theme, check out what I’ve done in functions.php of this child theme.