Forgot to make new database for civi... how uninstall?
You can remove civicrm.settings.php and run the installer again.  Here's where to find it:


Backdrop: &lt;webroot&gt;
Drupal: &lt;webroot&gt;/sites/default
Joomla: &lt;webroot&gt;/components/com_civicrm
WordPress: &lt;webroot&gt;/wp_content/plugins/civicrm


Note that this will NOT remove the old tables from your existing database.  To do that, see here.