1) In order to check what kind of prefix used by current installantion you can goto
wp-config.php in a root directory and find line with
$table_prefix = 'PREFIX_HERE'; variable
2) Backup the DB before making any action!
3) Additionally check if other tables with different prefixes/name_patters are not used by badly-written 3rd party plugins. They may not follow a good-practice:
Do not hardcode the WordPress database table prefix (usually "wp_")
into your Plugins. Be sure to use the $wpdb->prefix variable instead.
4) Right after this done you can drop all tables using a UI mysql admin panel or using more advanced way:
a. Generate a DELETE query programmaticaly:
SELECT CONCAT( 'DROP TABLE ', GROUP_CONCAT(table_name) , ';' )
AS statement FROM information_schema.tables
WHERE table_schema = 'YOUR_TABLE_NAME' AND table_name LIKE 'WORDPRESS-PREFIX_%';
b. Perform generated result.