In the admin section of WordPress navigate to the Post with a gallery of images you want to modify.
There are 2 ways to access your uploaded images.
2) Click the image icon adjacent to “Upload/Insert (see below)
Add title, media, size and date to “Title”. (As you get to know WordPress, you may want to use the other options. For now, leave them as is.)
Repeat this process with all your images.
Don’t forget to do this or your titles will be lost and you will have to enter them again.
Once you have finished click “Save All Changes”, at the bottom of the list of images.
Because this is a “Gallery”, do not click “Insert into Post”
Exit the dialog box
and click “Update”.
Check your page by clicking “View Post”. The title, etc. only appears in the “lightbox”, not below the thumbnails.
Repeat to create more “galleries”.