As you may know, Arch Linux is a rolling release Linux system, meaning that a massive update gets released monthly, including all the updates that have been implemented in the previous month, so that the users that download ISO images get up to date systems.
The latest version available is Arch Linux 2016.04.01 which is available for both 32 bit and 64 bit architectures. Among the changes, it uses Kernel 4.4.5 LTS as default (despite the fact that Kernel 4.4.6 has been already released).
If you already have Arch Linux installed on your computer, just open the terminal and run the upgrade command:
$ sudo pacman -Syu
Or, using yaourt, if you have the AUR repository enabled.
$ sudo yaourt -Syua