Sorry I wasn't clear enough. We are using RM as downloads manager and have files located on our server and outside. Once I record some download URL I can't change it anymore if file destination changed for some reason. And there is no matter if it on our server or outside, editing is not available.
Permissions are fine, checked many times. I'm able to add an update only for resource but can't change download URL which was entered first time. Change option not available for my own resource and resources added by other people.