Before doing anything, back up your existing 4.4.4 system. Use TWRP recovery if available, or use dd commands via ADB. This allows you to restore if something fails.

Warning: Upgrading Android TV from 4.4 to 5.0 may not be supported on many devices; proceed only if the device manufacturer or a trusted custom-ROM community provides builds for your specific model. Installing unsupported firmware can permanently brick the device, void warranties, and lose data. Back up anything important first.

You have searched everywhere, but there is no Android 5.0 ROM for your specific Android TV 4.4.4 device. Now what?