Yes.

Firstly, show your Styles Pane, then put your cursor into a paragraph that uses the style settings you want. In the Styles Pane, right click on the style whose attributes you wish to change and choose to "Update <stylename> to Match Selection"

Once this has been done for your style series, you can then select all of your content and press Alt-Shift-Right Arrow to demote all the headings one level.

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Andrew Lockton
Chrysalis Design, Melbourne Australia