[ Jeffrey Lee Li @ universe ] $ man life

Synchronization is made so simple and flexible by archlinux that one can easily be addict to it, like me. It's even more convinent than apt-get which is already trival. Unlike what some OS forces users to do what it should have done like searching the installers, dowloading them, maybe also need extracting them, then "simply double click" them, blablabla. What make things even worse is the incompatibility of various versions of the same program, which is no surprise 'coz the plaza in which these toys play breaks often without a reasonable reason, let alone those poor toys. The result is that every user pays the bill with amount of time, energy and money involved. Realizing that, what will you choose: the dangerous wood house with only windows and gates, or the fabulous solid-based tower.
Ok, enough for joking~:-)
Let's get to the subject of upgrading the entire system with every single tool installed.

sudo pacman -Syu

The -Syu options mean sync with the repo then upgrade everything.
Note that you need network and proper configured repo to achieve the result. And this is the recommended step to take after you've installed the OS and before any other installation happens. As we've said above, we just want to make our home cozy and comfortable.
Also note that pacman itself may be upgraded first, but don't panic, it can sync itself and detect automatically. So most times what we need to do is press enter to the default Y option.
We can run this a couple of times until it says there's nothing to do, indicating that we've been totally synced.
To make sure our operations are in effect, it's recommended to reboot the OS after the sync, especially when it's the initial setup or the kernel upgrades.