Currently I have Ubuntu GNOME 14.04 beta2 release. But in details it shows as Ubuntu 13.10. Please let me know how can I upgrade it 10 14.04 LTS final release(released 17th April). I tried in update-manager, but still it is not listing the new version.
You don't need to do anything apart from
apt-get update and
apt-get upgrade or simply wait until the new updates appear on the Update Manager. This will simply move your Beta 2 version to the final release. No need to download the ISO, reinstall everything or need to format.
So hold on a bit until Update Manager shows the new packages or do an:
apt-get update apt-get upgrade
And reboot. Enjoy 14.04 Final.