I forgot my password for my live installation. I searched the forums and found out, that you need to remove the user folders at
site/accounts. So I removed the folder, but after jumping to
panel/installation I could not execute the new registration due to the error Invalid CSRF token!. I cleared the cache (in the browser and in the site), cleared the sessions, but nothing seemed to work.
Finally I stumbled upon an error in the chrome console. I had set the security policy to
Header set Content-Security-Policy "default-src 'self';"- this broke the installation. I had to deactivate this setting to bring installation back to life.