Select all heading 1s (styles)

[magicmojo]

I mainly use OOoWriter to create e-books, converting them via Calibre is real easy.
Calibre uses the styles (Headings 1, 2, 3) to create a table of contents. Now, I'm making a book (copied lots of text from a webpage) and I've mis-applied the headings: they're all H1 instead of H3, meaning Calibre will mis-arrange the chaptering hierarchy, new page cut offs, etc.
Could anyone tell me how I select allstyles of H1, to convert them to H3?

[Bill]

Find and Replace has an option to search for styles.

[Alikiwi]

Normally with any books (print on demand) and ebooks, chapter headings should he H 2 I have found. Another way to change them, though slower is to simply highlight the heading, and right click and select heading style from the list.