Wait!! Wait!! Wait!! Go to your WordPress Dashboard not Dreamhost Dashboard!! You will be able to do all the things.[hr]
It's is much easier than what you are doing! You may install WordPress from one click install or using FTP, it does not matters. You need to go to your WordPress dashboard to install or un-install theme/plugins. It is much easier way to do things.
Suppose you install WordPress on http://myblog.com/blog/ than you should go to http://myblog.com/blog/wp-admin to login to your WordPress dashboard.
Probably you are new to WordPress! Please feel free to send me a PM on Studiopress support forum. My username (at studiopress support forum) is "AnandKumar"