I’m sorry, but I do not understand what you are asking.
What you need to do is to delete the directory named “installation” that is in your web site’s “main” directory.
You can use an FTP client, or the shell (via ssh) to do this. If you do not have an FTP client, you can use the DreamHost provided WebFTP program to do the deletion.
If this is what you want to do, you can click the “WebFTP” link for your domain in the DreamHost Control Panel -> Domains -> Manage Domains screen.
After you provide your password, you will be taken to the web directory where you can see, and delete, the installation directory using the WebFTP program.