Let's see if your answer is right. I had already done what you said and please enjoy the result as follows:

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
  nginx
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/426 kB of archives.
After this operation, 1,145 kB of additional disk space will be used.
(Reading database ... 100342 files and directories currently installed.)
Preparing to unpack .../nginx_1.9.6-1~trusty_amd64.deb ...
----------------------------------------------------------------------

Thanks for using nginx!

Please find the official documentation for nginx here:
* http://nginx.org/en/docs/

Commercial subscriptions for nginx are available on:
* http://nginx.com/products/

----------------------------------------------------------------------
Unpacking nginx (1.9.6-1~trusty) ...
dpkg: error processing archive /var/cache/apt/archives/nginx_1.9.6-1~trusty_amd64.deb (--unpack):
trying to overwrite '/usr/share/nginx/html/index.html', which is also in package nginx-common 1.8.0-1+trusty1
dpkg-deb: error: subprocess paste was killed by signal (Broken pipe)
Errors were encountered while processing:
/var/cache/apt/archives/nginx_1.9.6-1~trusty_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

The reason why it displays those errors is:

"From these errors it looks like the deb packages in the nginx repository are not packaged in the same way as those in the ubuntu official repos so there is a conflict between the new nginx package and the existing nginx-common package."

from https://www.digitalocean.com/community/ … sion-1-9-5

Stupid it seems, but I have no choice.

Thank you for your answer.