You'll have to roll-back gnome. Before uninstalling gnome, you'd better read Arch page on rolling back packages. If I were you, I would print this page.
Then, I would search for the earlier version of gnome that you would like to install, and I would procede with disinstallation only if I could really find the version I like. The Web page mentions strategies to find older packages. The simplest one is to search for the older package on your own machine, hoping you did not clean up your system too often. You can check this against the currently installed version, which you identify by means of
sudo pacman -Qs kde
Then I would download (if need be) the version of gnome you wish to re-install, without installing it. Then I'd go to a term (Ctrl+Alt+F1), and now procede to uninstall gnome and gnome-extra:
sudo pacman -R gnome gnome-extra
This saves the configuration files with a .pacsave extension, unless you use the --no-save option to pacman, in which case everything will be discarded.
Just for added safety, I would list the surviving gnome packages,
sudo pacman -Qs | grep gnome
and take note of their names (first), and then remove them.
At this point you should have a clean slate, and you may re-install the older gnome version.
The last thing to do is to persuade your pacman to skip updates of gnome. You do that by editing the /etc/pacman.conf file, and adding the following line:
IgnorePkg = gnome gnome-extra