[Karellen]

First you have to select your regex-function, in the "Function" box, then you have to fill in the "Find" box so the regex-function has something to work on. This is usually a regex based find.

Then it is no different to running a simple search or a regex search. Use the normal Find and replace buttons.

For example...
Find <h2>(.*?)</h2> This will find all h2 headings.

Select the function "Title-case Text"

Select Replace All (or find then replace if you want to do them one at a time) and it will convert all upper case headings to title case.