Teejay wrote : " ... If you have a clone backup of your wattOS (and hence a complete recovery option) then you could try the upgrade an see what you get.   I'd suggest first searching online for experiences of upgrading U from 14.04 to 16.04, so any major pitfalls can be avoided, but it would be an interesting adventure, no ? ..."
Damn right Teejay. That's what I intend to do in the future. Of course, I'm not completely stupid and I always make a clone backup of my system (thanks to Clonezilla) just in case I would want to get my wattOS-R9 back on track. But before that I'd like to make a clean installation of the new version of the brand new wattOS-R10 when it will be released. I'm looking forward for that, like all of us ! At that time, I won't have a lot to loose a lot. I guess it's worth trying and that's what I'll do later.

As you suggested, I've already written a few posts on two french forums to see what they think about that upgrade. For those interested, here's the link and the topic that gave the impulse to upgrade my Lubuntu 14.04.4 LTS to Lubuntu 16.04 Xenial Xerus :http://forum.ubuntu-fr.org/viewtopic.php?id=1884671&p=2
The interesting part starts at post # 48 written by Malbo. I forgot to tell you, it's in french but Google can manage the translation, right ?

Thanks for your detailled answer, Teejay !     

Hello,

I'd like to know if I can upgrade my wattOS-R9-32Bits from version 14.04 LTS to the new version 16.04 ? This is what I got in my terminal :

slyvester@slyvester-desktop:~$ cat /etc/update-manager/release-upgrades
# Default behavior for the release upgrader.

[DEFAULT]
# Default prompting behavior, valid options:
#
#  never  - Never check for a new release.
#  normal - Check to see if a new release is available.  If more than one new
#           release is found, the release upgrader will attempt to upgrade to
#           the release that immediately succeeds the currently-running
#           release.
#  lts    - Check to see if a new LTS release is available.  The upgrader
#           will attempt to upgrade to the first LTS release available after
#           the currently-running one.  Note that this option should not be
#           used if the currently-running release is not itself an LTS
#           release, since in that case the upgrader won't be able to
#           determine if a newer release is available.
Prompt=lts
slyvester@slyvester-desktop:~$ sudo do-release-upgrade -c -d
Checking for a new Ubuntu release
New release '16.04 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
slyvester@slyvester-desktop:~$
Thanking you in advance.
Slyvester