Sometimes, if you see a blank page after an operation, it might be a hidden warning. You can enable it for debug purposes by changing a special value
1. on the FTP, open /config/defines.inc.php
2. Line 28
define('_PS_MODE_DEV_', false);
change to
define('_PS_MODE_DEV_', true);
than you might see a php warning instead a blank page, that might help you to solve the issue