Most doors can be removed if you need to take them down to clean them. Frameless cabinets have a mechanism on the back of the cabinet-end of the hinge that releases the door and hinge from a mounting plate. Framed cabinets do not have this mechanism and should not be removed. They can be adjusted with a screwdriver, if necessary.
Shelves can be lifted out, and the shelf holders can be moved to adjust the shelves.
Drawers can be removed by grabbing them on either side and pinching a mechanism that attaches the drawers to the slides. Set the drawer back down, a little farther forward, and pull the slides forward until they click back in.