I have Centos 7 running in a virtual machine, Windows 8.1 is the host operating software and Centos 7 is the guest operating software, the Linux GUI is Gnome, but I want KDE is there a way to switch from Gnome to KDE after I have Gnome already installed.
There is a way. Once you install KDE, you can choose the desktop environment before you log in. In the log in screen, there will be a method to choose it somewhere, depending on the display manager installed
As @matazans had said, your display manager will usually show the desktop environments you have installed.
Also, may I ask why you're using CentOS as a desktop? Just curious.
The company where I work is slowly moving away from Microsoft and is replacing windows 8.1 with Red Hat. They recently singed a service contract with Red Hat, I know some one is going to pipe up and say Red Hat and Centos are great environments for servers but make terrible environment for Desktops. Right know we are only using Red Hat Enterprise for or servers. I didn't have any input on what Linux distro to go with our servers, but I finally convince my boss since I will be the one to retrain our workforce in Linux I get to pick the distro for our desktop environments.
Also since it is my job to not only to keep our servers running, but to train our workforce I wanted to find a distro that didn't cost anything for my home laptop that was as close to Red Hat Enterprise as I could get to avoid any confusion dealing with two different distros of Linux.
I am a fairly competent Windows Network guy, but have very little experience with Linux, so for right now I am trying to brush up my skill set to be that great Linux network guy. Since we are switching very slowly from Windows 8.1 I got the time brush up my skills before I have to worry about our desktop environments.
I'll chime in and add that you don't have to uninstall gnome to get KDE. you just run the command to install it. THEN you're able to choose your DE at graphical login.
Thanks I didn't know that I will try that.