OK your lazy susan is basically 2 round shelves on 2 supports that fasten to an adjustable pole in the middle.
First thing is to take everything out of the cabinet(s) to make this a lot easier.
the one that has a wobbly top shelf is either going to be a shelf that has loosened from the frame or a setscrew that loosened. look on the underside of the topshelf and you will see the platform that the shelf attaches to- is it loose? (you may need to replace some screws that hold the shelf to the support) there will be a set screw that tightens to the center pole. make sure it is tight.
The other one will bad bottom shelf do part or all of the following (depending on how low to the bottom you want it to be) the bottom shelf mounts to the center pole same as the top shelf) The set screw has loosened and you'll need to raise the shelf and tighten it.
TO REMOVE Look on the center pole and you wiil find a collar with a set screw, loosen this and the pole will fall into itself - then loosen the setscrew under the top shelf, andf the shelf will go to the bottom- now it can be removed from the cabinet. (you may need to fight with it a little) YOU DONT HAVE TO REMOVE IT unless you want to. Once you get it loose you'll be able to get at the bottom setscrew to adjust the shelf up and tighten the screw.
You may need to turn the shelf to get at the screws.
heres a generic picture http://www.kitchensource.com/lazy-susan/am-fullround.htm