Look on the bottom and top edges of the doors near the hinges. There should be two screws visable. If you unscrew these, the doors should pull straight off the metal tabs attached to the hinges. To put the doors back on, just reverse the process.
To update my cabinets, I lightly sanded, primed (w/ spray on primer) and then spray painted my YK cabinets & drawers. I used a gloss white (Krylon, I think). Almost 7 yrs on they still look great. Make sure you wear the proper respirator and have good ventilation! Another friend took her entire YK kitchen ensamble to an autobody shop and had them strip and repaint them. They look fab!