For example, you might want a different font color for one of the existing heading styles. A great way to make the change is to update the style based on actual formatting in your document.
To change the heading style based on a selected example:

Select the heading and make the formatting change, such as a change to the font color.

In the
Styles task pane, point to the style, and click the arrow on the right to display the style's menu.

Then, click the
Update to Match Selection command.
Everything that has this style updates to reflect the change.