Upload bp-branded-login folder to wp-content/plugins directory
Login to WordPress backend
Go to Dashboard->Plugins->Installed and look for "Branded Login for Buddypress"
Activate the plugin
If you are using BuddyPress 1.5+, Please create pages for login/logout/reset password(You will see a notice at the top of the wp-admin, once you activated this plugin)
Assign the pages to Login components in the BuddyPress->Pages screen