This is a page from the Flash Renamer user manual.

Find & Replace

The Replace function allows you to look for a certain string within filenames and replace it with another string.

    All your filenames have underscore "_" instead of spaces!
    Use the Replace function and enter "_" in the search box and " " (space) in the replace box to tidy up your filenames! (Note: Do not type the " characters.)

Batch Replace

With Batch Replace you can run several Replace commands in one go! Use this for replace operations that you perform all the time. You can modify the list of replace commands from the Settings window. You can also add the current Replace function settings to the list by pressing the button with an exclamation mark! You can add multiple items at the same time if you use the Settings Window.

Note: By default the batch replace list is loaded with words that often need to be corrected! It is recommended that you go through the list before using this function, so you know what words are included.

    You want to replace "Im" with "I'm", but not if it is part of another word, e.g. "Swimming".
    Add a space " " before and after both words, like this: " Im " and " I'm ".