A. On the Front viewport, draw a selection rectangle as shown in the image below:

B. Change to circular selection and while holding the ALT key, draw a selection circle from the center of the rim to almost the outer side as shown in the picture below to deselect all of the polygons except the ones on the outer side of the rim.

C. You should now end up with the polygons being selected as shown in the image below:

D. On the Front viewport, scale the polygons up on the Y-axis.