For those with multiple styles, this is what you need to do.
1. First of all locate the file
discuss.css from the files you have downloaded on here. It is located in
discuss/css.
2. Next make a copy of the file and rename it to whatever you want, for the purpose of this tutorial I'm going to call it
custom.css.
3. Now to edit the new CSS file.
I've made this image to get the novices started, however it's taken me a bit of time just to knock this demo up, so if you want to do all the pages your either going to have to work it out or ask for help with the CSS.
4. So, now you've edited your CSS file and are happy with it, upload it to root/discuss/css.
5. Next go to
Admin CP-->Styles & Templates-->Style Manager, now select
Edit Templates from the dropdown menu in the style you want to edit. Scroll down the list until you find
discuss Templates, double click and look for
discuss_main.
Now find
discuss/css/discuss.css and change the path to point at your new CSS file, in this case it would be
discuss/css/custom.css.
Hit save and you should be all done.
If you find that you need to make further edits, you can usually do this on the fly via your FTP Client.
If you need any help with this just ask.
Good luck.