I checked similar question here but not got an answer. I upgraded to elementary os from ubuntu 16.04 and now want to migrate it back. Have anyone successfully done so?
Update: I don't know exactly how it got upgraded from ubuntu 16 to elementary os loki. I was just tryining pantheon-desktop . After installing I remember did apt dist-upgrade and magically had elementary os loki name writter in my next reboot instead of ubuntu 16
The latest version of elementary (0.3 Freya) is based upon ubuntu 14.04 Trusty LTS so I'm not sure a "downgrade" is really what you are after here as you haven't strictly "upgraded" in the first place. eOS is a different "flavour" of Linux, it's more of a cousin of ubuntu 16.04 Xenial than it's progeny.
If you took Ubuntu and installed various packages such as pantheon-desktop, midori browser, or scratch-text-editor you may be able to use sudo apt-get remove <package> to remove these and restore the ubunty unity desktop, etc.
However, if you installed elementary from a bootable USB, this is a fresh install and you would need to repeat this entire process with a bootable ubuntu USB. Note that it is highly recommended to back up your files before proceeding with this.
There is no option for downgrading by default. A fresh install is always the best solution. Downgrading is possible but very problematic.
For more information:
ppa:elementary-os/dailyto the Ubuntu 16.04 system (like in this unhealthy post). That is not Loki, as Loki has not been released at the time you are posting, is just the highly unstable elementary os daily repository on top of Ubuntu 16.04. - That was not properly speaking an upgrade, as Loki is to be based on 16.04 anyway, it's just mixing repositories and adding unstable packages to Ubuntu 16.04, and going back to your clean Ubutu 16.04 is not a downgrade, but a difficult cleaning job.