Not only do you not need to uninstall a previous version, in fact you MUST not do so if the module has been used at all on your site (and text/html module is probably the most commonly used of all modules). If you uninstall a module from your portal, all instances of the module are removed from your site (from the web site pages, that is), and content in them is lost.

So you are correct - simply install the new version of the module and it will update your current version without loss of data. You are altering the database during many if not most upgrades, as well as the file system. It's good advice (which I don't always follow) to back up both file system and database before module upgrades, much as one does before a DNN framework upgrade.

You can generally get some information on the newer features or changes of a core module in the projects area of this site. That said, I tend simply to keep up with core module releases most of the time (with a reasonable lag to see if others are reporting issues).