[Plugin: WordPress.com Stats] Changing primary domain

Before launching my website, I built it in a separate directory. Whilst testing stuff, I installed the wordpress.com stats plugin. On wordpress.com, my primary domain was bananasaboutmovies.com/mb

However, I’ve since moved all the WordPress files to my root directory, and now I want to change the primary domain, in my wordpress.com dashboard, to just plain bananasaboutmovies.com. Can’t seem to do it from my wordpress.com dashboard. And if I do, does that mean I need a new API key? Am I allowed to even have one? How does this affect Akismet?

If I’m honest, I find the whole thing a bit confusing. ??