You may be looking the media caption and properties via the Derived Properties view. That is the media item is inheriting its caption and properties from the media library. If you need to change the media items global properties or caption you can change the view to the ‘Library Properties.
Or if you only wish to make a change to this one instance you can set the Media Object Derived property to True.
From the Help…
Media Properties – Inherited vs Derived
It is important to understand how media is handled in Fact Sheet Fusion. When media is added to a project via the Media Manager , default properties such as watermarks, copyright, photographer and caption etc can be added against the media. This information and the properties associated with the media are automatically available when attached to a Topic, Entity or Glossary Term. This concept is referred to as inheritance. This saves you from having to enter the same information over and over again each time the image is reused. However there are circumstances where the properties and information associated with a media item need to be customized. If these changes are not global in nature; and you don’t want these changes reflected in all the other instances where the media is attached, you can set the attached media item to be derived.