Hello. Download the version you want to [http://www.getfirefox.com getfirefox.com]. See [http://www.mozilla.com/en-US/firefox/all.html here] for all languages and systems. Then you uninstall your current version and install the new one. No data will be lost. You can also install the new version in a different location, without uninstalling your old one, and you'll have two different versions of Firefox, using the same [http://support.mozilla.com/en-US/kb/Profiles profile].