OJS 3.x does not support direct upgrades from all prior versions. If your copy is extremely old, you may need to upgrade first to an intermediate version.
In order to upgrade from these older branches of OJS, you will first need to upgrade to an intermediate version of OJS 2.4.x. Download the latest copy of OJS 2.4.x and follow the upgrade instructions included there, then read the docs/UPGRADE document included in this package to continue the upgrade from there.
Upgrades from OJS 3.0 Alpha and OJS 3.0 Beta to OJS 3.0 are not officially supported; neither release is intended for production use.