- launch the Windows Registry Editor by searching for “regedit” from the Start Menu or Start Screen
- Computer\HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\edit\command
- Right click on the (Default) key and choose Modify
- Change “%systemroot%\system32\mspaint.exe” to “C:\Program Files\paint.net\PaintDotNet.exe”
No need to reboot or log off and back in.