Is it possible to update a version in iTunes Connect between 22-29 December? If it is, could somebody tell me how to do it?
Thanks!
No, as the Apple announced they are closed between 22-29 December. You will not be able to upload new version of your app.
You could have easily found this yourself by check the link about why they are closed: https://itunespartner.apple.com/en/apps/faq/Managing%20Your%20Apps_Submission%20Process#68611491
What iTunes Connect, Application Loader, and Transporter features are unavailable during the holiday closure? From December 22 to December 29, 2015, the following features will be unavailable:
- App submissions for new apps and app updates
- App bundle submissions for new bundles and bundles updates
- In-App Purchase submissions
- TestFlight submissions for external testing
All other features, and access to iTunes Connect, will still work.