Hello,

all is explain on the site in Technical aspects for upgrade.
https://www.projeqtor.org/fr/product-fr/technical-fr/51-setup-fr/397-product-setup-fr  

Your database will have updates depending on the version, but it doesn't impact your data already stored in it, or it will be only minor changes for improvement or patching .
However it is always better to have a backup of your database.

Thanks for your feedback,
in a webinar it was mentioned the fact that we could make a backup without the plugin how to make such a backup? thank you

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merci pour votre retour,

dasn un webinaire il a été évoqué le fait que l'on pouvait faire une sauvegarde sans le plugin comment faire une telle sauvegarde ? merci

and how to make a backup without buying the plugin sold?
I was told in demo that it was possible. Thank you

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et comment faire une sauvegarde sans acheter le plugin vendu ?
il m'a été répondu en démo que c'était possible. Merci

Hello,

if you don't use the plugin Backup Database, you had to do it manually with the tools of your database. 
The ways to do this vary depending on the type of your database (mysql, postgres)

thank you
where can we find the information for this?

You can find this information in your database manager's documentation.
You need technical skills for databse maintenance if you want to make a database backup..

good you won

 It's not a game.
ProjeQtOr is a web application, so to maintain it you need to have minimum technical skills to maintain a web server, including backups.
It is to ease this point that we developed the backup database plugin, to ensure that even not "technical skilled" teams have the opportunity to backup their data.