Updating existing calendars
You can update most information about a user's calendar via the owncalendars feed. You'll need to parse out the calendar entry's edit URL. This URL is found in the <link> element where the value of the rel attribute is edit:
<link rel='edit' type='application/atom+xml' href='http://www.google.com/calendar/feeds/default/allcalendars/full/calendarId"></link>
To update the calendar, send an HTTP PUT to the edit URL with the updated calendar <entry> element in the message body. The following entry will update the calendar's title and color, and mark it as selected:

