One way to switch to a Ubuntu gnome is installing ubuntu-gnome-desktop metapackage. But, that you give you two DEs aren't much pure. Unity settings sometimes causes problem in Gnome-Shell and vice versa.
To completely remove all components of Ubuntu and install Ubuntu-gnome instead, I suggest using this script. The script was developed by the person who was providing the command for these kinds of Switching till 15.04.
- Download the
purebuntu.py file from this GitHub repository.
Install the apt-rdepends package using the terminal command
sudo apt-get update && sudo apt-get install apt-rdepends
Run the purebuntu.py file using this syntax:
python purebuntu.py --remove ubuntu-desktop --keep ubuntu-gnome-desktop
This will generate an apt-get command which will remove Ubuntu related packages and install ubuntu-gnome-desktop metapackage.
This will give you a fairly clean Ubuntu gnome desktop. Take note though, You might lost already installed extra packages because of this operation.
P.S.: You can generate the commands to switch back using:
python purebuntu.py --keep ubuntu-desktop --remove ubuntu-gnome-desktop