Model number of the Sharp would help also. Just replaced my Sharp R-1874 convection microwave. It had two long bolts in the bottom at an angle that needed to be loosened then two screws in each side of the case ( not factory) then you hinge the microwave down and lift it off the mounting bracket. All screws ar only visible if you remove the grease filters in the bottom of the microwave. My motorhome has a has a spice rack above the microwave that just sits on the top of the microwave and had to be removed first but it was not screwed in.
Brian, Loretta & Daisy (Golden Retriever)
2008 HR Endeavor 40 PDQ , ISL 400
2010 Dodge Ram 1500 Toad