Your theme consists of nothing more than a set of (mostly) PHP files.
You have to figure out which file the offending line is in and open that up in a text editor.
In the best case, you will see the line straight away and be able to delete it.
More likely however is that the file will
include another file and/or the line you are looking for is generated by a PHP command.
Which theme are you using.
If you can post a link to your site where I can see the line you want to delete I don't mind taking a look for you (as long as the theme is free).
N.B. It's late here and I'm off to bed, so I won't be able to pick up this thread until tomorrow.