Newbie Q: Next/previous text link on image attachments page

I love the design on https://Ma.tt
I’m new to php and WordPress, and Matt does a lot of awesome customizations that I’d like to figure out how to do.

For instance, I really want to modify the Zack 990 theme so that on the image attachments pages I can have a text link ABOVE my photos that say “next picture” and “previous picture” in text (example). (Currently the theme has clickable photos at bottom and the text isn’t an actual link — or I could just copy it to the top).

Here is an example of the unmodified theme’s attachment page.

Can someone help me with the code I need to insert to get a TEXT link to the next/last picture? Thanks.