All good advice so far from the others. I have removed both of mine, during a total tear out nearly 4 years ago. In my case I remember screws and 1/8" pop rivets. I drilled out the pop rivets with a #30 bit. It did take some searching to find them all out, but once all the fasteners were removed both cabinets popped right out without damage. As suggested, a helper is nice especially for the over the sink cabinet. In my case there was a single hard to see rivet inside the upper portion of the sink med cabinet that needed to be removed.
I just looked at my old med cabinets. I counted 4 holes on the toilet wall cabinet (2 in the inside right and two on the outside left) and 4 that would have been holding the above sink cabinet (3 along the bottom exterior and 1 inside upper middle).
I also suggest dealing with lights and wiring first, before you try to remove the cabinets. Post pictures of your installations if they are like mine I can definitely be of more help.
Virginia Beach, VA
1992 29' Excella Classic
TV 2006 Dodge Ram 2500
Mega Cab Diesel 4x4