Are you saying you want to proportionally increase the selection size?
If so, when making the selection HOLD Alt + Shift while dragging.
Or do you mean that you want the portion of the pixels selected above to increase in size?
If so, select the desired pixels. Copy/paste to a new layer*. Select the Move tool. HOLD Alt + Shift and drag away from center to increase size.
*Pro Tip: Always use a separate layer for non-destructive safety measures.