Hi Cindy - Welcome to the Articulate community!
It's all done in the states. Select the states view (beside the timeline tab) then select a circle. Double-click on its Selected state and it will open the states to edit. The text is just in the circle shape itself, so just drag to select and replace the text.
Right click on the image and you'll see 'Replace image' in the menu that opens. And that's it.
To change the disc colours, change them in normal view (not in state-editing mode) and it will change at least the disabled colour automatically. Then once you're in state-editing mode, you can change the others.
I'll maybe do a quick video when I'm back at my desk.
Have fun with it!
Jennifer