upload your banner image to the directory called banners in your cpanel
let's say the file name is newbanner extension is gif . so banner name will be newbanner.gif
and link will be :
"
http://www.sitename/banners/newbanner.gif"
now open the directory called members and find the file called banners.php inside it
find his code :
$bannerlist=array(
"
http://www.$settings[domain_name]/banners/banner1.gif",
"
http://www.$settings[domain_name]/banners/banner2.gif",
"
http://www.$settings[domain_name]/banners/banner3.gif"
);
add your banner link in following format :
"
http://www.$settings[domain_name]/banners/newbanner.gif"
if you placed the banner as last banner , make sure you add , at the end of the banner before it
the missing of a , would show error in the banners page , so check it carefully

good luck