Tell us some details. Like ... what happens when you try, and what error message(s) appear (please quote the complete error message, word-for-word, verbatim)
Thanks for your reply the verbatim of the message is : impossible de mettre à jour cette collection. impossible de contracter le service Flickr .Veuillez vérifier votre connexion inernet.
This error is supposedly caused by Lightroom internet interface (assuming nothing wrong with Flickr server).
Is Lightroom able to connect to other internet services? e.g. map module, or export-to-ftp..
If not, then you got a larger scope of system problem to solve (try rebooting computer first, if you haven't already). If so, then time to investigate Flickr, plugin and/or service..