For this you need to understand the naming convention of tpl files in Drupal. This link will help https://www.drupal.org/node/1089642
According to documentation,
"http://www.example.com/node/1/edit" would result in the following suggestions:
page-node-edit.tpl.php
page-node-1.tpl.php
page-node.tpl.php
page.tpl.php
Either you can try adding content-type in the naming as suggested(I have not tried it personally), or if there are few customization to be done, adding a check like
<?php if($node->type == 'content_type_name') ?>
over available variables in "page-node-edit.tpl.php" will also do.