Blogger has given bloggers using their platform for their blogs the option of leaving the blog as a
sub-domain of blogspot.com or become a custom domain using the blogger's domain.
While custom domain has lots of advantages, it however suffers from the disadvantage cost wise of having to bear the annual renewal of the domain.
Now, if you no longer want to bear the cost, just how can you revert the custom domain back to the blogspot sub-domain?
The solution is to sign into www.blogger.com (Dashboard), click the down arrow at the top right corner ,
and in the BASIC > PUBLISHING section
just click the X icon (highlighted in red above) and the custom domain is no more and the blog will revert to the original blogspot sub-domain URL.