Not if you do an upgrade (download 1.9.3 from this site, upload all the files to your server, in your browser goto http://www.yoursite/blogs/install/install.php and choose for upgrade rather than a clean install.)

Your database with your posts will not be lost; the database will be upgraded though.

If you made changes to your skin or if you employed hacks you must redo these on your new install. Therefore (and for other matters) you should always make a backup of the existing files (and of the mySQL database as well).

Read more on this topic in the [url=http://manual.b2evolution.net/Upgrade_from_an_older_version]manual[/url]

Just don't be afraid :)

Good luck