After a post office is upgraded to GroupWise 2014, users who have accounts in that post office can start using the GroupWise 2014 clients. You can give users access to a GroupWise 2014 software on the GroupWise download page, so that they can install the GroupWise client themselves, or you can use the other methods of client software distribution described in Distributing the GroupWise Client
in the GroupWise 2014 R2 Administration Guide.