Apple Watch is a brand new product line, which has a completely independent ecosystem, on par with the iOS Device and Macs. The company also seeded a new watchOS 2 for developers in the WWDC 2015 event that recent held.
Typically, to use this new watchOS 2, you should be an Apple developer member, a privilege that now extends across all platforms for only $99, then download and install WatchOS 2 manually.
idownloadblog give us a simple tutorial on how to install WatchOS 2 update.
Then pair your Apple Watch with this iPhone for installing.
Note: Charge the Apple Watch at least 50% and keep it connected to its inductive charger throughout the installation process.
How to Install
Step 1: Download the watchOS 2 beta Configuration from the Apple Developer portal directly to your iPhone, you can also download the watchOS_2_beta.mobileconfig.zip form this third-party link without a developer account.
Step 2: Launch the profile, tap Apple Watch as install location and reboot when asked
Step 3: Launch the Apple Watch app on iPhone
Step 4: Tap My Watch → General → Software Update
Step 5: If requested, enter your passcode
Step 6: Wait for the Apple logo to appear and watch the progress bar fill in completely
Step 7: Your Apple Watch will reboot once the update is completed.