Hi Astro2,
It's very easy, actually.
If you already used OP before, write down your settings or do screen shots of the settings pages.
Download the software from here:
https://librepilot.atlassian.net/wiki/display/LPDOC/DownloadsInstall the GCS, start the GCS. When you connect your controller, it may most likely give a warning that the firmware does not match. So go to the Firmware and press update&erase. This way your controller gets updated.
After that go through the setup wizards to get your multicopter up in the air. If you have already done some fine tuning, apply the setting using your screenshots.