How to edit part of the gallery (wp gallery no plugin)

Hello all, ok so ive just been told by my client that, on the gallery, the pictures’ name and description are on the same line.

so for example if the picture is called ABC, and the description is 123.

the output is “ABC-123” all on one line.

She wants the name on one line, and the description on another, like so:
ABC
123

problem is that, i dont even know what im looking for as far as how to edit the code, on the output id just enter a quick br tag or something but, again, i dont knoow where.

any ideas on where this is?
im using the latest build of WP

Thanks in advaced