I figured it out, but it was a long process. I got help from C.A. staff, but I still had to stumble around and find some things for myself. Here is what I eventually found to work:
Build Menu>Wall>Break Wall to choose limits of wall area to change.
Then go to Edit MENU>Select Objects>to select this desired wall section between the inserted breaks.
After selecting object, the Edit TOOL PANE (not drop down menu) will appear. Use Open Object tool, a Wall Specification dialog will open.
Scroll down list on left side of the dialog to “Wall Types.” A drop down menu line will appear within the Wall Spec dialog. Use it to choose the type of wall to replace the selected section with. Select OK and the new wall type will be inserted.
Previously I had been trying to use Build>Wall>Define Wall Types to start drawing a new wall in the old section area. It didn't work, and I didn't need to draw a new one, just change the area I selected with the process above.
Thanks (and my signature should show up now with my system info, too)