Maybe it's a deliberate choice to have the text [Edit Media] on the button instead of the [Save Changes] text that we can find when we edit a profile comment or thread posting? But as a first time user overhere of the XFMG for me the default Xenforo text [Save Changes] is more logical and intuitive than [Edit Media].
The reason is that when I see a button labelled [Edit Media], one thinks this is the action that will be performed when pressing this (action) button. But we are already in the action process of 'editing the media', as the title of the dialogue box clearly displays. After editing the media one wants to perform the action to save the changes and therefor it would be more logical and intuitive the button reflects this. Next to that it would be more consistent with the rest of the XF userinterface.