How to update Luxeritas in Lightsail (bitnami)
// download thema file
$ wget https://thk.kanzae.net/wp/download/path/to/luxeritas-x.yy.z.zip
// backup now version thema
$ cp -rp apps/wordpress/htdocs/wp-content/themes/luxeritas ~/luxeritas~
// install new version thema
$ sudo cp -rpf luxeritas apps/wordpress/htdocs/wp-content/themes/
// modify owner
$ sudo chown -R daemon:daemon apps/wordpress/htdocs/wp-content/themes/luxeritas
Note: Only cli. No operation in wp-admin.
Ref: thema download page