oki doki, lemme start from the beginning so i don't get confused.
in your FTP program, connect to your website.
in the directory where you keep your forum, open the folder "templates"
upload the subblack3d folder into the templates folder.
now, go to your forum, and access your admin panel.
in the category "styles admin", choose "add"
after subblack 3d is installed, go to general admin --> configuration
under "default style", click the dropdown box and choose subblack 3d. this will make it the default. also choose 'override user style" if you want it to stay subblack and don't want people using the old subsilver.
hope this helps..!