Under the EDIT menu, select KEY MAPS, and the keyboard map will open
 

Press KEY TO MAP, press the button on the keyboard you want to change, and click CHANGE MAP (in this example, we will map the Control key for the Field Plus function)
 

Press the FUNCTION button, scroll down to Field Plus and highlight it with the mouse.  Press the ACCEPT button. 
 

Repeat steps 1-3 for any other key you would like to map. 
 

After you have finished, press the SAVE button, and then press the DONE button. 
 

Then go to the FILE menu, select SAVE USER SETTINGS.