What is the passcode so i can update the iphone

We can't tell you what your passcode is. It's the one you set up on your iPhone and it's encrypted directly on the phone, so even Apple can't tell you what it is.

You will need to fully erase your iPhone if you own iPhone 6 Plus as your tagline suggests if you don't know the passcode. See this link for directions --> If you forgot your iPhone passcode - Apple Support

This will require using a computer with iTunes (Windows) or Finder (Mac).

Only you know the passcode to your phone. If you have forgotten the passcode, You will need to restore the device using a computer. The process will erase the device. Later you can restore your data from a recent back-up. Instructions here…

If you forgot your iPhone passcode - Apple Support