Hi @Ramsin_Shahedi,
I would not suggest using the OJS 3.0 beta. We’ve made a lot of progress since then and will not be officially supporting e.g. upgrades to/from the beta release. It’s not intended for production use.
We’ll be releasing OJS 3.0 this summer, i.e. soon, so I would suggest either waiting for that release or using the stable release of OJS until then. There will be an upgrade path from 2.4.x to 3.0.
Alternately, you can install OJS pre-release code from github, but we can only provide limited support if you run into trouble.
Regards,
Alec Smecher
Public Knowledge Project Team