The latest Arnold version is 18.104.22.168, but that's not the version number we use for licensing. Arnold licensing uses the Arnold release date (yyyymmdd) as the version number. For example, if you have a license for version 20140512, you can any version of Arnold released before 12 May 2014.
To check the release date of Arnold, just set the verbosity level to Warnings + Info and do a render. The release date is printed at the top of the log. In this example, the release date is 2014/06/23, so you need a license with version greater than or equal to 20140623.
If you're using kick, just run kick with no arguments.
If you don't have a license that can run the latest Arnold, you'll see something like this in the Arnold log (as long as verbosity is at least Warnings + Info):
This says that you need a license for 20140623, but you have only a license for 20140529. The version 20140529 in your license is either the date you purchased the license or, if you were on support, the date your support contract expired.