LaserWeb4 is the latest and recommended control software.  

Installers are linked here:

Further documentation is available at:

Here are screenshots of the Settings:

1. Machine Settings.

The K40 has an X of 300mm and a Y of 200mm.  

The origin is at 0, 0 and there are no offsets by default. 

The beam is 0.1mm for an expert user.  Beginners may want to start with 0.2mm  Realistically, the range for this is 0.1mm and 0.5mm, some degree of de-focusing (using a larger beam diameter) can help with rasters.

2.File Settings.

Note that the PXPI and DPI values are dependent on the software you export these from.  Default values are shown here.

3. Gcode Settings

4. Application Settings. 

A note about "Feed Units": This is entirely a personal preference and will vary from person to person.  This is what units are used to talk about the speed the machine moves at. If you hear someone talk about cutting at 5 or 20, this is mm/sec (millimeters per second).  Alternatively, if you hear someone talk about moving at 6000, this is probably mm/min (millimeters per minute).  Just multiply or divide by 60, respectively, to convert between the two.