Short answer: no! :)

Long answer:

The posts, comments, users, settings, etc. are stored in a MySQL database which is not part of your b2evolution file structure. It is next to impossible to accidentally overwrite and erase that data. It is even quite hard to delete your database on purpose.

The uploaded files (images, etc.) are stored in the /media directory and its subdirectories. When you upload the new files, the files you have uploaded there will typically not be impacted. If you are worried though, just make sure you do not upload the /media directory when upgrading.

The last critical file is /conf/basic_config.php. This file contains the location, login & password information to your MySQL database. Accidentally deleting this file can ruin your day if you need to figure out your MySQL password again (you generally never use it directly). The b2evolution distributions do NOT contain a fresh copy of /conf/basic_config.php so it’s still quite hard to overwrite it by mistake. (The file is created by the installer during the first install).

So basically it’s very hard to lose your data, but, just to be safe, we still recommend you make a backup of your MySQL database as well as your files (if nothing else, at least the /conf and /media folders) before you upgrade.