The Designer automatically resizes the toolbar to fit the items you place in the toolbar.
If you want to increase the size of the toolbar, simply move one of the items in the toolbar down, so that part of it is past the lower edge of the toolbar. The Designer will automatically adjust the size of the toolbar to fit the item.
Alternatively, click the baseline of the toolbar and drag it down to a new position. The cursor changes to an up and down arrow icon. Release the mouse to set the size.
Parent topic: Toolbars