How to "demote" all titles and headings in Word 2010?

Alternatively, you can go up to the "Styles" panel in the ribbon and right click the desired style, and click "Select All", and then simply pick a different style.

Under the "Home" ribbon, in the "Editing" section, select "Replace".

You may need to select "More" to see all the options.

Put the cursor in the "Find what" field. At the bottom, click the "Format" button. Select "Style". Select the style that should be "demoted". Start with the lowest level style in the document (ie. don't start at the titles). Note that the style will be shown below the field, not in the field.

Put the cursor in the "Replace with" field, and follow the same instructions to select the style that it should be demoted to.

Click "Replace All" to update the styles. Run through each of the styles.