If you want to alter a style, but you don't want to permanently alter original styles in your document's template, create a completely new style.
Here's one way to do this: If you're creating a new heading style, select text with the heading style you want to alter, and make the formatting changes to it, such as a bigger font size, different style, and different color. Then:
Open the expanded Quick Styles
Select Save selection as a New Quick Style
Rename the style in the Create New Style from Formatting
You'll practice creating a new style at the end of the lesson.
Tip Another way to create a new style is to click in the document, in the actual style you want to build the new style on. Select the down button next to the Quick Gallery to display the expanded gallery and select Save Selection as a New Quick Style.