As you may know, Arch Linux is a rolling release, 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.
Arch Linux 2015.12.01 has been released today and brings security packages, package updates and various optimizations. It has kept Kernel 4.2.5 as default and updated X.org server to version 1.18.0, among others.
If you already have Arch Linux installed on your computer, just open the terminal and run the upgrade command:
$ sudo pacman -Syu
Or, download Arch Linux via the kernel.org mirrors or via torrent.