You can do it in several ways. If you have an ftp program then you set it up with the address of "upload.comcast.net" (no quotes) and your username and password, and then you can upload all of the files generated by Photoshop. When you go to your webspace, it will have an address like:
where "yourusername" is your actual comcast username. The little squiggle in front of the username is a "tilde" "~". When you go to the address a file called "index.html" will be loaded in the browser. This file may not have the gallery that you've just created referenced. By default the Photoshop Gallery maker creates a "index.htm" extension. If you change that when generating the gallery you can choose ".html". When done, copy everything that it generated to your wite and then it will show up. There are three folders created as well as 4 or 5 other files.
Unfortunately the Comcast support and documentation of using the webspace is very limited. They don't even show you how to use ftp. But here is their FAQ page that answers some questions:
It is actually not too hard to do, but you do need to go through a number of steps.