To update a platform to a superior major version (from version 21 to version 22 for example),
You just need to click on the "Update available" link just on the right of the platform major version.
On the next page, just specify the version you want to update to.
And finally, you can specify the date and time you want this update to be done :
- At a specific date and time (this date and time must be specified in your local time)
Validate this page and confirmation, and your update starts..
This update takes around 10 minutes.