Drag to Resize

Select the stencil(s) you wish to resize.
If you wish to maintain the stencil's proportions, locate and click the aspect ratio lock in the Transform controls in the toolbar or right-hand sidebar.
Click and drag any of the stencil's resize handles (white squares on each edge and at the corners).
Drop the handle when your stencil is the size you desire.

Note that this method will resize the stencil in increments related to the grid size. For more granular control, decrease the grid size or use the dimensional controls as described below.

Resize with Dimension Controls

Select the stencil(s) you wish to resize.
If you wish to maintain the stencil's proportions, click the aspect ratio lock as described above.
Locate the width and height controls in the toolbar or right-hand sidebar.
Type the desired dimensions or click the up and down arrows in the width and height control fields.

Select the stencil you wish to resize to fit its label text.
Locate resize to fit controls in the Transform controls in the toolbar right-hand sidebar.
Click the Resize Horizontally to Fit control to adjust stencil width.
Click the Resize Vertically to Fit control to adjust stencil height.