I'm assuming you used the first option in the answer. To uninstall the 3.4 kernel and keep using the 3.2 kernel:
You will have to boot into the 3.2 kernel first, so you are not removing the kernel you are currently using. To do this, you will have to select the appropriate kernel on boot from the Grub menu. If you do not normally see the Grub menu, hold down Shift on boot, and it will appear. Using the arrow keys, scroll to "Advanced options for Ubuntu [version number]" and press Enter. Then scroll down to the latest version of the 3.2 kernel, which is 3.2.0-40 if you have that latest version installed. Make sure not to pick Recovery Mode.
Once you have booted, open up a terminal and remove all versions of the 3.4 kernel with:
sudo apt-get purge linux-image-3.4.0-* linux-headers-3.4.0-*
This will not require that you install any additional software such as Synaptic, it will simply remove the kernel. After rebooting, the kernel will be uninstalled.