When you click on the "Edit" tab at the top of the admin page, you should see a list of all the albums. If you want to edit the text for the pictures in one of the albums, click on that album's thumbnail.
You should then see a list of all the images in that album and you should be able to change the text for each picture in the album.
From you screenshot, it looks like you may be clicking on the "Mass edit all album data" link instaed of an individual gallery thumbnail.