Version 6.1.7 is faster than ever and has full compatibility between desktop and web versions. Whether you're using Tracker online or locally you can save TRZ project files that will open identically in most platforms and browsers. (If you have not looked at Tracker Online recently you should check it out at https://physlets.org/tracker/trackerJS/ You can maximize it in the browser with the up-arrow button at the right end of the toolbar.)
To upgrade, click the green "Now available" button on the toolbar and choose Upgrade Now. If you don't see the green button choose Help|Check For Upgrades.
You can also download installers directly from the Tracker home page (http://physlets.org/tracker/) or ComPADRE (http://www.opensourcephysics.org/items/detail.cfm?ID=7365).