Sounds like you should be editing the Master Pages.
In most cases, the graphics are image files and can only be edited in the native graphics program that they were created in, such as Adobe Illustrator. They are probably JPEG EPS or PDF format that were placed into the image box. Of course, they will show in the Links panel just like a photo. Hope this helps.
As I read this, you are having trouble selecting the images so you can choose "Edit Original" or perhaps reposition or replace them. The edit or replace functions can probably be done by selecting them in the links panel, if you are lucky enough to actually know the names, but let's figure out why you can't select them.
Possibility 1 is, as Larry suggested, that they are on a master page, but that seems unlikely to me, so possibility 2 is the frames are locked, and you haven't change the default preference to prevent selection of locked frames. Possibility 3 is that they are on a layer that is locked, in which case you would need to temporarily unlock the layer in the Layers panel.