Enter the text you want to replace in the Replace box.
Uncheck Replace to leave the text as is, changing only its font, size or colour and alignment. In this case, the Replace and Replace All buttons will be disabled until you choose a Font, Size or Colour change to make.
To set the Font, Size or Colour you wish to use for the replacement text, click on the reflow line, align auto hyperlink.
Notes
To do font replacement with this dialog (rather than using the Replace Fonts dialog), uncheck both the Find and Replace checkboxes and set up character formatting for both the find and replacement.