How to update PLEX server (QNAP TS-451 NAS)

1. when you start the PLEX webapp, an orange bar says there's an update
2. click the link and download the qpkg file to your computer
3. open QNAP NAS web interface
4. go to AppCenter
5. choose "Install Manually" (upper right corner)
6. choose "Browse" and find downloaded file
7. click install