I removed the upper rack with a phillips screwdriver by removing four of the glides wheels. The glide bar that is attached to the rack is held in by two white plastic retaining end, simply twist and pull. ( note: you do not have to remove any glade wheels to remove upper rack )
While I had both racks out of the machine I clean debris that accumulated in the filtering area by removing hex nuts ( varies with each model ) with a nut driver. I also checked to see if water flow from the spray arms were clear ( top & bottom )
Reinstalling went quick, I just followed the reversal of my disassembly