Our server on Server Beach recently was upgraded to SFTP.
Needless to say, I don't have access to PORT 21/FTP. How can I change that to the appropriate port?
Why are you using FTP to upgrade rather than the built-in http?
Because the HTML page requires FTP loggin and password for it to upgrade.
I think it uses it to access the backend.
No it doesn't. Those fields are there in case you need to use FTP versus HTTP. But almost any site that is configured correctly and has correct file/directory ownerships can be upgraded without using any of the FTP credentials.
It is far better to upgrade with HTTP since you will ensure that the files are all owned by the PHP user that is accessing your store. If you use FTP, then it might be a different username and some of the dynamic creations may not work properly.