Did you just install the minimal version by accident or want to install the GUI? No need to reinstall just tell yum to do the work for you!
You could actually have both installed and choose one as your preference on demand (although many people prefer GNOME's simplicity).
Install Gnome and/or KDE.
To install the GNOME Desktop on Centos 7:
yum -y groups install "GNOME Desktop"
I've used rsync again for this because I found it very simple, I've only excluded the Cache directory since it's not necessary and could be several GB in size.
rsync -Phaz --exclude=Cache/* email@example.com:/home/user/.mozilla/firefox/profile.default/* /home/user/.mozilla/firefox/ec1n9opl.default/
This is a great way once again to get going how you were on the old/remote computer fairly quickly. It even restores all of your history in........