Slab Modification is now done using the Modify Slab dialog. This dialog can be found by using the universal 'Modify Properties of Selected Elements' tool (3D Modify Tool Box>Modify Properties of Selected Elements) and selecting the Slab you desire to modify.
You can also activate the tool by selecting the Slab, Right-Clicking, then selecting Modify Slab.
The Modify Slab dialog box displays the catalog entry name for the selected slab.
The property values displayed are those from the selected slab.
All fields in the Apply/Edit column are checked and property values are enabled for immediate edit.
More on this can be found within the AECOsim Building Designer HELP by searching within the Search tab for Modify Slab dialog box.