500 Internal Server Error after Upgrade

Changing permissions and ownership for files needs to be done in your control panel or by your tech staff (web host support) if you cannot do it in your file manager.

Very true. We all tried and can’t do it.

Whoever owns the server *can* change the permissions. They need root access. If you don’t have root, you don’t own the server. Contact the server admin for help. Most likely you are on shared hosting, so you would open a ticket with your web host. If it’s a VPS and you have root, then you need a person who knows how (e.g. chown and chmod).