Go to https://github.com/triplea-game/triplea/releases/
Click on the latest version (the top post).
Under “Assets” there should be a set of links. Click on the one that fits your computer (if you use Mac, click on the link with the macos, Windows, the one with windows in it, etc.).
Click on the file in Downloads. It should open up a TripleA downloader similar to the one you used when you first downloaded TripleA. It should open (if there’s an error, it’s probably on your end).
It’s a vast improvement over 2.5 but is very easily navigable.