If you are this low on memory, the best choice would be to switch a lightweight Desktop Environnement (DE), such as:

- [XFCE](https://www.xfce.org/)
- [Mate](https://mate-desktop.org/)
- [LXDE](https://lxde.org/)
- [LXQt](https://lxqt.org/)
- etc.

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](https://fedoraproject.org/wiki/EPEL), 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.

[![login screenshot][1]][1]

  [1]: https://i.stack.imgur.com/mlBMe.jpg