The title screen of fileRename

Click start to get to the main screen.

The first thing to do is find the files you wish to rename.
Click 'the disk drives' to start navigating your computer.

A list of your drives comes up. Double click one them to see the contents.

Folders appear in the left box. Files in the right one.

Double click on folders to see the contents.
The current path is shown in the box labelled 'current path'.
To go to parent directory click the button next to 'the disk drives'.

Once you've found the files to rename, you can add them to the list by double clicking on individual ones, or (as in this case) clicking on the big arrow to add all the contents of the current folder.

The list of files appears in the 'Files to be renamed' box.

If you wish to copy the files into a new directory before renaming them now's the time to do it.

Create a new folder by entering the new folder's name and then clicking 'new'.
Then select the new folder by double clicking on it.

After making sure the 'from' and 'to' paths are correct...

... click 'copy to'.

These images are currently in the wrong order.
In this case they are best sorted by number.

The files are now their correct sequence.
If you need to sort the files more exactly, you can clear the box by pressing clear and then add them individually by double clicking on them.

Type the new name in the boxes at the bottom.
The second box contains the start number. If you want more (or less) lead zeroes you would start from 00001 (or 1).
The third box contains the extension. It is vital to get this right otherwise your files may become unusable. For this reason it is unwise to rename batches of files with different extensions.

The last step is to click 'rename as' to perform the rename.

The new files in all their glory. The lead zeroes mean that programs like afterFX will import the images in the correct sequence.

The original files are as they were.

There is a help file with the program for additional assistance.