How do I set/change the default printer on my sunray (in sun java desktop)?

you can change your default printer by using the sun java desktop preferences tool, as follows:

Click Launch
move the mouse to the Preferences entry in the list that pops up
click Printer Preferences in the Preferences list that appears
this will launch the Printer Preferences pop-up window

in the pop-up window, you will see a few printer icons
one of them will have a green check mark on it
that is your default printer

to make another printer your default printer:
click on the icon for that printer
click Printer -> Set as Default

to see more printers:
launch the Printer Preferences window
click View -> Select Printers to Show
choose some from the list or click Select All
click OK