If your current WordPress database table prefix is the default “wp_”, use "Rename WordPress table prefix" tool to change it.
This tool is accessible from the site you're managing, under the "Security" tab.
Before you rename the database table prefix, you have to confirm that you have taken a backup of your database and wp-config.php file (the prefix is stored within this file).
You can have a valid, recent backup of WordPress here.
To rename, simply enter a new prefix into the field (see the screenshot below).
For more information on changing the WordPress database table prefix, read the blog article here.