MU site, two blogs with one root

Hi all! I have a WP MU site (complete with content already), and I would love to change the URL of the second site to be on the same “level” as the original one. For example, currently the “primary” and “secondary” blogs are at:

https://www.example.com/blog
https://www.example.com/blog/secondary

but I would like:

https://www.example.com/blog
https://www.example.com/secondary

Is this possible with MU? I’ve tried setting the URL through the admin panel and it seems to take, but no luck — the primary blog is displayed at that URL ??

Any help??

Thanks,
-elliott-