Apple has released watchOS 2, the first update to the Apple Watch’s software. Originally scheduled to be released last week, it was pushed back because of an undisclosed bug.
To install the software, go to the Apple Watch app on your iPhone, and tap General > Software update. Note that to update the Apple Watch, it must be connected to a charger, in range of your iPhone, and must be charged to at least 50% before you start. Be aware that updating the Apple Watch takes a long time; I think when I installed the GM (gold master) of the software, it took more than an hour. This is because transferring data to the Apple Watch uses Bluetooth, which is quite slow.
If you have already installed the GM of this software, be aware that there’s a new 12 MB update waiting for you.