A good security tip when installing your Wordpress blog is to change the database table prefix, the idea is that this will hide the tables from any hackers looking to compromise your blog. This can be done in the wp-config.php file and the variable $table_prefix. Changing this value from the default wp_ to, for example, blog_ will change the table wp_posts to blog_posts, making it more difficult for hackers to find it. Using blog_ is only an example, you should treat the prefix like a password, include letters and numbers to make it more difficult to find.
But what happens if you have installed your system and want to change the prefix? Well you need to change the $table_prefix variable in your wp-config.php file and alter the tables in your Wordpress database. Which one you do first is up to you, but you should go them both as fast as you can. Here are some MySQL statements that should help you to do this.