Hi ted burke,

If I am visualizing your problem accurately (see attached) you will need to change all the walls because all the angles (between the walls) will change
Anyway, if the angles are not a concern, just select a segment--> delete the segment--> add new walls

Regarding the foundations and levels, to visualize the concepts, perform the following test:
Create an empty file (File--> new)--> Go to the floor tab--> you will see a small arrow at the right of the name. By clicking the small arrow you have the option of view / hide other tabs--> click in the small arrow--> the floor tab will be selected--> select also the foundation tab--> draw an exterior wall--> go to the properties bar--> be sure the foundation is selected--> in your plan, you will see the wall + the foundation--> put a window / door, etc--> Go to the foundation tab--> click on the small triangle--> foundation tab will be selected--> select the floor tab also--> your plan will look in the same way in the floor tab and in the foundation tab, right? --> Now, in the foundation tab--> click on the small triangle--> unselect the floor tab--> the wall and the foundation will disappear!
This means that you can draw a wall with or without a foundation, but you can't draw a foundation without a wall. If you draw a foundation, as this step includes a wall, and the you draw a wall, you will be duplicating the process

Patricia