Hey mate, i've never used Hanthana, but i just looked it up and it seems to be based on Fedora, if it uses Fedora repositories, then any command valid for Fedora should be Valid for Hanthana too. This is handy to know because Hanthana is not a major distribution, so you may have trouble finding help for it. Fedora is a major distribution though and finding help for it may be a lot easier, and then the advice can be transferred to Hanthana.
Try the following command.
sudo yum groupinstall "GNOME Desktop Environment"