A stable version of Linux Kernel 3.9 has been released recently which brings more new features such as SSD caching, full support for Chrome OS, better support for ARM SoCand, faster LZO compression, and  more drivers for better support for modern computers. Linux 3.9 has also brought improvements to networking, storage, virtualization, power management, etc.
You can find the release announcement here

cd /tmp
wget http://dl.dropbox.com/u/47950494/upubuntu.com/kernel-3.9 -O kernel-3.9
chmod +x kernel-3.9
sudo sh kernel-3.9
sudo reboot

To remove kernel 3.9, enter this command:

sudo apt-get purge linux-image-3.9*

To remove or to revert back to the earlier Kernel enter the command below:

sudo apt-get purge linux-image-3.9*