[CentOS] upgrade from 6.5 to 7

I installed centos 6.5 from a dvd.  Now that 7 is out, I'l like to try it.  I tried:

sudo yum  clean all && sudo yum update

but it said there were no updates.  Is there a command-line way to upgrade from 6.5 to 7?

Thanks,

-wes