PDF (adobe.com)

Edit slices by moving slice guides

Slice guides define the perimeter and position of slices. Slice guides that extend beyond slice objects define how the rest of the document is sliced upon export. You can change the shape of a rectangular slice object by dragging the slice guides that surround it.

You can't resize nonrectangular slice objects by moving slice guides.

Resizing a slice object by dragging its slice guides

Note: If you drag slice guides that surround a Fireworks button in the document window, Fireworks resizes the slice that defines the active area for that button. You cannot delete the active area for a Fireworks button by dragging the slice guides that surround it.

If multiple slice objects are aligned along a single slice guide, you can drag that slice guide to resize all the slice objects simultaneously.

Resizing multiple slice objects by dragging a single guide

If you drag one guide along a given coordinate, all other guides on that coordinate move with it.