Content File can delete only its owner, you're right.
Why you need to delete it? It's not necessary to delete files.
If you need to delete files - you can use CustomObjects module for this http://quickblox.com/developers/SimpleSample-customObjects-ios#Files
Custom Objects has Permissions API http://quickblox.com/developers/SimpleSample-customObjects-ios#Permissions , so you can set proper permissions and delete record by any user