You can download the JS file from your banner page. Just go to the Installation tab and find a section called "Download and host banner yourself".
How to upload a file to your server?
You can upload files to any folder on your website or to a root of web directory. This can be done using an FTP client or any other method you use to upload files.
How to use files on your website?
If the file is placed in the root website directory. Change the file name to the one you have uploaded. Or:
If the file is placed in the “includes” directory.
You can change the file name to your own if you need.