why is that I do not get the option to edit the footing size. attached plan for ref. current size is 16", i want to change it to 12"
221016.plan
If you are using automatic deck framing, you can specify the default size for your footings with the other deck structural controls.
If you are manually editing your deck framing, then your footing is just a slab with two arcs. You can edit the size the same way you would any other polyline based object. One quick way to resize it would be to use a concentric resize.