[CentOS] Upgrading to CentOS-7 on a new partition

I would like to upgrade a CentOS-6.5 home server
to CentOS-7 on a new partition.
What is the simplest way to achieve this?
I would like to be able to boot into either version of CentOS
until I am sure the new version is running OK.

Incidentally, I think most people today must have enough space
on their hard drive to install a new OS on a new partition -
it is surprising that this option never seems to be mentioned
in upgrade documentation.

-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin 2, Ireland