Once you go to the modules > material specification, firstly select the material specification in the dropdown window and then click the edit material specification icon on the top. This will enable the edit mode.
Some notes on editing material specification are as follows:
Clicking the edit material spec icon;
will make the selected specification editable.
Now in the right side of the page you can edit the material specification. Double click on any text on this side to change the specification name. Double click on any image to change the image. Make sure to add images in the type *.BMP. If you have images of other file types (ex: .jpeg, .PNG), you can open the image using paint and then save it as *.BMP type.
To add or remove material specification entries, you can use the options on the top of the edit specification section. Once you have done, ensure to click save on the right side and then also make sure you select the specification from the dropdown in the left and click the green check mark to assign it to your current project.
You can refer to the Material Specification Editor section of the HGA user manual for more information on this: https://www.waterloohydrogeologic.com/help/hga/using_hga_menu_bar_project_modules_material_specifications.htm?zoom_highlightsub=material
Hope this helps!