The location of the installed Maxwell Render application can be set in a dialog which is located under Edit > Preferences > Maxwell Render Settings… in the menu.
The dialog expects the location of the Maxwell and Mxed executables. When the path changes the plug-in verifies if the given file exists and displays an error message if not.
If the MAXWELL3_ROOT environment variable is set then the plug-in will use it by default and no manual settings are needed.
The settings are stored in the maxwell.pref file located in the HOME/houdini[version] folder.