Change Default WordPress MU Blog

I have a wordpress multisite installation and a default blog under / (let’s call this blogZ). I want to create e new blog called blogX and set it as the default one.

The blogZ should appear under /soccer path.

This is what i tried to do:

1. clone default blog: impossible, there isn’t any option for the default blog.
2. change default blog in wp-config.php, working on define('BLOG_ID_CURRENT_SITE', 26); and also doing a try changing define('SITE_ID_CURRENT_SITE', 1);. NO RESULTS

How could we solve the problem?