Good to hear Plex is stable.
Moving to the c:\ drive is straightforward.
To move the Plex application, just uninstall and re-install, telling Plex to install to the C: drive.
When you uninstall, use the standard Windows uninstaller (Control Panel → Programs & Features or Settings → Apps). Do not use Revo, CCleaner, or any similar uninstaller program. You want to uninstall just the program, leaving the Plex Data Folder and registry entries intact.
Then, re-install the software. Run the installer. The first window has an Options button. That lets you select the location for Plex. Enter the default location, C:\Program Files (x86)\Plex\Plex Media Server, then proceed with the installation.
When Plex Media Server starts, it will see the registry entries telling it the Plex Data Folder is on your J drive.
Make sure all your libraries, shares, etc are OK. Then reboot the server just to make sure the changes will survive a reboot. Once you’re satisfied the system is stable, you can move the Plex data folder.
Moving the Plex Data Folder
See this guide: [HowTo] An extended guide on how to move the Plex data folder on Windows
It shows how to move the Plex data folder from the default location to a custom location. You’ll do the same steps, but move it from your J drive to the default location, C:\Users\<username>\AppData\Local\Plex Media Server.
