1- In that specific x3d file, the yellow x and its ring were imported as a single object, while the other rings were imported separately. If you need three rings, just copy one of the existing ones, and make that yellow. You can then add text or import other objects.

2- You can select a ring and change its size from the menu bar in the font size field, usually it says "Fit to width". You can change this to 5%-400%. If you adjust something this way, then you may well find you have to do some repositioning as well, by varying line sizes and/or adding space characters on one side or the other of an object.

Mike