You can only delete manually created styles.
To delete a style:
1.Select one or more paragraphs to which this style is applied, or select part of such a paragraph, or place the cursor in it.
2.Open the style list in one of the following ways:
•On the Home tab, in the Styles group, click the
button.
•Open the Styles pane.
3.Hover the mouse cursor over a style and click
Delete style.
After you delete a style, all paragraphs with that style will default to the Normal style.