Here are the necessary steps for deleting an installation of Koken from your web server.
Delete the Koken admin folder
Using your FTP client, sign-in to your web server and delete the folder containing the Koken admin. For most users this folder will be labeled "/koken". If you uploaded Koken's installation script to a folder labeled something else, delete that folder. If you uploaded Koken's installation script to the root of your domain you would need to delete every file and folder you see there that was not created by you.
Delete Koken's database
Using your web hosting provider's control panel, delete the MySQL database that was created when Koken was installed.
Delete Koken's additions to .htaccess
If you edited the URL field in Settings > Site Publishing so that Koken's web site is published outside of the admin directory you may want to clean up your .htaccess file. To do that, first check to make sure your FTP client is displaying invisible files. Most FTP clients have a preference/setting for this somewhere. Once invisibles are turned on, browse to the directory where your Koken site was published and make a backup of your current .htaccess file by dragging it to your desktop. Edit your .htaccess file by removing the entire code block labeled "Koken", as illustrated below.
Save your .htaccess file.
After following these steps all files and markup created by Koken should be deleted from your server.