Frequently asked questions - Writer
From The Document Foundation Wiki
How do I modify the style/format of a title?
The default style/format of Heading 1, Heading 2, or Default style is easy to modify.
To update it:
- Display the Styles and formatting window using ▸ (F11);
- Select the text which already has the format you want;
- In the Styles and Formatting window, click the button on the top right New Style From Selection;
- Select Update Style.