If you use the tape and simply measure a distance and then type in a new dimension, then SU will prompt you whether you want to resize the whole model.

As bmike said, you can double click the component, measure a distance and type in a new dimension, hit return and just the component will be resized.

In your scenario, using the scale tool and sizing by eye is probably the easiest way to go about it. If you hold the option key down while scaling, it will scale about the center, which will keep the component directly above/below its current location. A simple move action, locking the blue axis and you are good to go.

Cheers, Chuck