The latest version of appium can be found here. Currently, 1.6.2 is the latest but does not have a GUI version available. You can install it using npm.
If you want to use the latest GUI version available, it can be found here (1.5.3) but be sure to read the release notes to make sure it will be compatible with what you want to test.
Also, a very small amount of research could have gotten you all of these answers… google.com is your friend.