Format arrow styles, line weights, and color choices to alter the look of connectors.
Change the look of a connector quickly
Select a connector.
Select Home > Quick Styles.
Select a style you want.
Format a connector
Select Home > More.
Select a connector.
From the Quick Styles menu, select Line and then format what you want:
Select Color and choose a color for your line.
Select Width to make the line thinner or heavier.
Select Begin Arrow type or End Arrow type to change the look of the line endpoints.
Source: Microsoft