I know, this is an old post, but since it pops up as the first result in Google when searching for "Windows Swap Audio Channels", I thought it would be good to post a working, free solution here:
- Download Equalizer APO from https://sourceforge.net/projects/equalizerapo/
- Configure it to attach to your output device (Usually something like: "Speakers - VIA HD Audio" or "Speakers - Realtek HD Audio"); you can change this later with the "Configurator" tool from the Equalizer APO start menu folder
- Create a new file in C:\Program Files\EqualizerAPO\config, name it for example swapchannels.txt
- Paste the following line into it as its only content:
Copy: L=R R=L
- Save it
- Open Equalizer APO's configuration editor
- Make sure that your device is the correct one in the dropdown menu on the top right
- If applicable, remove all pre-configured options by clicking the red "minus" icon (or, if shown, the button with two arrows pointing downwards, then "Remove")
- Click the green "plus" icon to add a new configuration for your output device, then navigate to the "Include configuration file" option
- Select your swapchannels.txt file
- Save/Apply the configuration
Install and configure EqualizerAPO for your output device with only one configuration file that has only
as its content.
Hope this helps!