How to change element type in ANSYS Workbench 2023 R1

While using WB the element selection is somewhat limited. In order to use a shell element you would need to be meshing a surface geometry and not a volume. If you have defined a given thickness ie. defined the in and outer boundaries of your surface WB will mesh it with solid elements which is why you are getting brick elements. Most modeling software (Solid Works, Inventor, etc.) define a volumetric model. You would need to redefine you geometry in space claim or design modeler at the mid surface for the shell as the thickness will be applied to either side of the surface. If you are utilizing a simple geometry it may also be easier to select element type/geometry using an APDL script with a command line input if you are familiar with that method.