Problems upgrading Ubuntu 12.04 LTS to 14.04 LTS

Hi to All,
I’m new to ubuntu and I’m tring to learning. What I need is upgrade ubuntu version, but I have some difficults.

I’ve seen many suggestions around the web, but no one helped me.

The problem is that when I run:
sudo do-release-upgrade

the result is:

no update found

I tried

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install update-manager-core

but running

sudo do-release-upgrade

same results

i tried with -c
same
with -d
same

I think there is something wrong somewhere, but I cannont understand it by myself.
I’m using an Ubunt desktop virtual machine on a vsphere 5.5 with opne vmware tools installed.

running lsb_release –a
Distributor ID: Ubuntu
Description: Ubuntu 12.04.5 LTS
Release 12.04
codename Precise

Thanks in advance for help.

I’d recommend using one of the official support channels listed on the Finding Help page.