uploading themes

Hi, I know I might sound stupid here but I have a (really) basic question. I’m trying to upload a new theme onto my website, but I can’t because I’m putting in the wrong info. It’s asking for: 1, Name of Host; 2, User name; and 3, Password. I’m doing something wrong but I don’t know what. The host is the name of the company we are using for our domain rego and maintenance, yes? If so, how do I type that in, as their website name or as just the name of the company? And finally, do I use the username and password given to me by them, or is it another combination?
Please help this first timer!! I’m trying to learn as I go but I can’t even get to the batting plate!! hahaha
Thanks in advance.
Mick,
SpotOn English