1 : backup database (using copy with phpmyadmin for instance)
2 : disable all extensions
3 : run upgrade as described in release anouncement
composer update --prefer-dist --no-dev -a --with-all-dependencies
php flarum migrate
php flarum cache:clear
4 : rename flarum webroot directory to flarum_bak
5 : install a fresh flarum as described in installation notes
composer create-project flarum/flarum . --stability=beta
6 : rename fresh flarum's public and storage directories in fresh flarum folder to public_bak and storage_back
7 : copy flarum_bak public and storages directory into flarum fresh one.
8 : be sure to copy also .htaccess files
9 : make sure permissions are good in the flarum directory (chown www-data:www-data may be needed after copies)
10 : resinstall your personnal extensions with composer (language pack, etc.)
I hope it will help !
