You can do most of this via WebFTP in the panel here. Go to Domains -> Manage Domains and click WebFTP next to your domain name.
From there, you can upload your pictures. I suggest you create an organized file structure for your newsletters, like /newsletters to drop the html files in, and /newsletters/images for the pictures.
While in WebFTP, you can manually edit your html newsletter files to update the path and filename for the images you uploaded.