When you select an item, black square handles appear on it. You can resize an item by clicking and dragging these handles.

While the dimensions of a wall or symbol are shown, you can click on a dimension and type a new one in its place. When you press the Enter key or click somewhere else, the item will automatically adjust to reflect the new dimension you entered.




You can change the units and scale of the dimensions displayed on the Work Area (How?).
Another way to resize the item more precisely is to select it and use the increase/decrease buttons in the Position & Size group on the Design tab to specify the exact height and width of the item.

To resize the item just a little at a time, select it and hold the Shift key; then use the arrow keys to expand the item in that direction, one pixel at a time.