If you are this low on memory, the best choice would be to switch a lightweight Desktop Environnement (DE), such as:
If you are (even sort of) new to Linux, I would suggest you to stay away from Tilling Window Managers (TWM), although being extremely lightweight and powerful once configured and mastered, I do not think one of these would be a good idea given your situation.
If you want to install XFCE (example):
First, you need to add the Extra Packages for Enterprise Linux (EPEL) repository, as this is where you will install packages from:
# yum -y install epel-release # sed -i -e "s/\]$/\]\npriority=5/g" /etc/yum.repos.d/epel.repo # set [priority=5] # sed -i -e "s/enabled=1/enabled=0/g" /etc/yum.repos.d/epel.repo # for another way, change to [enabled=0] and use it only when needed
Then you can install XFCE Desktop Environment as following:
# yum -y groupinstall X11 # yum --enablerepo=epel -y groups install "Xfce"
After a reboot, you will be able to switch to XFCE4 instead of using GNOME3 at the login screen.