Hi @redukr
The “files” table only exists in OJS 3.3. If your upgrade is complaining about it existing already, it sounds like you had a failed upgrade to 3.3 before, and then did not completely restore your database from a backup (you perhaps just reloaded your old one, which would not have dropped the files table). The table should not exist in your database prior to your upgrade to 3.3.
The inability to create foreign keys means that your OJS database user does not have the REFERENCES privilege within MySQL. OJS 3.3 now creates foreign keys in some places and you will need that, as well as also ensure that you’re using InnoDB database tables rather than MyISAM ones. MyISAM tables do not support foreign keys.
Best,
Jason