what to test
rpm -e --nodeps glpi nethserver-glpi
Check messages logs /var/log/messages
Thanks in advance
I tried to update as per Stephane’s instructions, almost everything worked.
The difficulties I encountered and I would say solved were 
The old plugins were not visible in the “plugins” menu, I solved by downloading the new package with the wget and consequently I expanded them into the old folders of the plugins. At the end of the procedure, the system showed me the complete list in the marketplace menu.
I have revised the rh-php.ini file of rh-php73 due to the resignation limited to uploading and posting documents and files worth 500 MB.
The images of the user profiles were lost, so I had to restore them.
Many associated documents such as images, pdf documents, etc. probably did not open due to an external link to the file. In fact, by reloading the attachments, the GLPI server displays or downloads the newly uploaded files.
I had to re-execute the PC inventory, because the upgrade to the package did not take into account the inventoried data, but the list of computers was present. Therefore, I upgraded to the server for each PC.
At the moment everything works, including call notifications, then new ones, updates, etc.
upgrade from 0.90 (nethserver-glpi) to 9.5.7
We need to write down some notes I think 
Of course, but it would be appropriate for someone else to proceed with the version update to get feedback on the same problems.
The update from nethserver-glpi to the new nethserver-glpi-latest ran without errors. 
I can confirm that the user images and files are not there anymore after the update because they are removed from /var/lib/glpi/files at uninstall of the epel glpi. I tried to save the files before removal and copy them to the new location /usr/share/glpi/files but without success.
Thanks @mrmarkuz, so we can confirm what I wrote. Is it possible to remedy the problem in your opinion? Thank you as always.
Fun because they are not owned by the rpm :-?
OK, the files are not removed, there were errors because I moved them away manually 
So the files from glpi 0.90 are still in /var/lib/glpi/files after remove.
Just the folders are owned by glpi:
[root@testserver2 ~]# rpm -ql glpi | grep files
/usr/share/glpi/front/filesystem.form.php
/usr/share/glpi/front/filesystem.php
/usr/share/glpi/inc/filesystem.class.php
/var/lib/glpi/files
/var/lib/glpi/files/_cron
/var/lib/glpi/files/_dumps
/var/lib/glpi/files/_graphs
/var/lib/glpi/files/_lock
/var/lib/glpi/files/_pictures
/var/lib/glpi/files/_plugins
/var/lib/glpi/files/_rss
/var/lib/glpi/files/_sessions
/var/lib/glpi/files/_tmp
/var/lib/glpi/files/_uploads
What did you do to fix the file upgrade ?
I didn’t correct the update of the missing files, but being a small number and backup to other PCs, I reloaded them. Certainly this is in my reality, but imagine a server with lots of documents and more … 
Ok I have a fix I think
I made a typo in fact
0.90 stores files to /var/lib/glpi/files
9.5.x stores files to /var/lib/glpi
if you copy /var/lib/glpi/files to /var/lib/glpi
yes | cp -rf /var/lib/glpi/files/* /var/lib/glpi/
then images/document become available
what to test
rpm -e --nodeps glpi nethserver-glpi
Check messages logs /var/log/messages
Check you can login as before
Check all data are migrated from /var/lib/glpi/files/* to /var/lib/glpi/* (you can access documents/pictures)
Thanks in advance
No errors, login worked, profile pictures and pdfs are viewable now after the update. 
I wanted to thank you for taking charge of the problem of GLPI old version, @mrmarkuz and @stephdl for their commitment to GLPI upgrade tests.
I think GLPI is an asset that deserves a lot of attention!
thank, we will see if we obsolete nethserver-glpi
released