Image Gallery Management improvements (delete selected image nodes)

Hi!

First sorry, but I new in drupal.
I want improve the image gallery management module, to be able mass delete selected image nodes, but when I declare function node_multiple_delete_confirm, than say redeclare error, but when I not declare, than say that the function is undefined.

How to able use this function (node_multiple_delete_confirm) from gallery_manage.module and delete the nodes with selected nid?

Thank you for help, and for lesson :-)