You need to change the stroke and fill for the object.
Select the object and press Ctrl+Shift+F to open the Fill and Stroke window. On the Fill tab, change the fill to No Paint for transparent. On the Stroke paint tab, change the stroke to a solid color. If you want to change the thickness of the outline, go to the Stroke style tab, and change the width setting.
Source : Link , Question Author : Vitaly Zdanevich , Answer Author : Scribblemacher