Assuming you would like a step-by-step guide on how to update your Apple Watch to iOS 6:
Before you begin, make sure your iPhone is updated to iOS 8.2 and that it has the Watch app installed. Once your iPhone is all set up, open the Watch app and tap My Watch. Next to Software Update, you should see Download and Install. If an update is available, tap Download and Install. Otherwise, you'll see Your software is up to date.
Now for the actual process of updating your watchOS. First, place your Apple Watch on its charger and keep it there until the update has finished. Make sure your iPhone is in range of your watch during the entire process—the two devices need to be communicating with each other during the update. Second, on your iPhone, go back into the Watch app and tap My Watch > General > Software Update. You should see Download and Install appear next to an available updates; tap it. The update will now download onto both your devices; when it's done downloading, a prompt will appear on your iPhone asking if you want to install the update now or later. Choose Install Now (it might take a few seconds for this option to pop up). Once installation begins, don't disconnect either device or close the Watch app—let everything run its course until completion. Depending on how much data needs transferring and installing, this could take anywhere from five minutes to half an hour or more; when finished, both devices will restart automatically. After that's done…you're all set! You should now have watchOS 6 running smoothly on your Apple Watch!