"Un-installing" WordPress if you're not worried about saving any of the data you might have entered (warning: you will lose everything, so backup if you're not sure), is a simple 2-step matter:
1) Delete all WordPress files. If you installed into your root directory, delete all the files and directories installed by WordPress (wp-config.php, /wp-content/, /wp-admin/ etc). Be careful to not delete any other files you might have had there before WordPress. If WordPress is in a subdirectory, simply delete the subdirectory and all its contents.
2) Go into PHPMyadmin or whatever else you have on your server to edit MYSQL databases. Select the database used by your WordPress install and drop all the WordPress tables. Again, if this was a fresh database only used by WordPress, you can drop all tables. If the database had existing tables before, make sure you don't lose them.
WordPress is now un-installed and you can use the same blank database with the old settings to install it again.