There's 2 way to get back to running a stock WDTV ...depending on custom firmware type you're using.
First Method: If you're using the flashdrive inserted method (2.02.32-EXT3_Palace_Plus-0.1.4)
then simply double the win-homebrew-stockify.bat script then check the homebrew is disabled by clicking win-homebrew-status.bat ... if all good, then power off the WDTV and remove the flashdrive
Second Method: If you have "flashed" custom firmware on your WDTV ... then the first thing you need to do if find out what version you are running.
eg. on your WDTV Remote, press SETUP button, then select ABOUT ..... you should see something like this ....example: 1.02.21.WDLXTV_LIVE-0.4.2.0
Now ... download any Official WD Firmware (does not matter if it's the oldest or newest)
Once downloaded ... open the wdtvlivegen3.ver using Microsoft Notepad (or any word editor)
you will see something like this ....
Now, if you are running WDLXTV (as per the exmaple above ... 1.02.21.WDLXTV_LIVE-0.4.2.0)
You need to edit the Official WD Firmware "version" to Exactly that, BUT with a Higher Number (to trigger the "Detected New Firmware" prompt on the WDTV
Example: Editing the WD Firmware *.ver file
Save and close Notepad .... then go through the normal firmware flashing procedure (don't worry about version numbers the WDTV reports)
At the end of a Successful WD Firmware Flash ... if you check Setup > About, you will see the WDTV will report the correct Official Firmware Number