MAKE A BACK OF THESE FILES:
admin/categories.php
admin/includes/languages/(Your-Language)/categories.php
catalog/product_info.php
catalog/popup_image.php

Copy the one's from the contribution over the old ones

add the new file/s
catalog/includes/modules/additional_images.php

run the SQL script into your database with PHPMyAdmin or other DB Manager...

All Ajax Attribute Manager Files should already be installed previous to this installation.

Just upload the files in the attached zip overwriting the old.

More...