By default, the Line Style toolbar contains quick access tools to change the line attributes of the currently selected markup(s). These tools will be unavailable/dimmed when a markup with no line attributes is selected.
If the toolbar is currently hidden, go to View > 
Toolbars and select it to show it.
The leftmost element in the toolbar shows a preview of the current line style. In the sample toolbar above, the style is a solid, 1-point line.
Start Style:Sets the graphic style for the start of the line, such as a dot, block, or arrow.
End Style: Sets the graphic style for the end of the line.
Line Style: Sets the style for the line itself, including solid and six dotted variations.
Line Width: Sets the width (in points) for the line and its ends. Use the Line Width setting in the Properties tab to set values that are not included in the list.