Basically
1) Download as Ipython file from the File Option
2) Use notepad to open the file downloaded. Copy the text contents
3) Create a new gist at by pasting the text from step 2 here
https://gist.github.com/ (assumes you have a github account)
4) Paste the url of the Gist into http://nbviewer.ipython.org/ to get your iNotebook url for sharing
5) To update your notebook, simply copy and paste the new IPython code by editing the gist again
6)
(example here- http://nbviewer.ipython.org/gist/decisionstats/62c5387624a9ba9015a4)