In order to play the new expansion for Factorio, all you need to do is update your server to play version 2.0.7 or version 2.0.8 (both are supported)
If you create a new Factorio server, it will automatically use the latest version supported - which will include Space Age.
For existing servers hover over the Actions button on the dashboard and select Update. A box will now appear showing the version you will be updated to. Click the button and you're ready to play.
To select a specific version, see our tutorial here: https://help.serverflex.io/how-do-i-change-factorio-version-or-branch-on-server/