You would need to reconfigure the site B as a replication partner of site A, using Mgt. server reconfiguration wizard, and overtie the database at site B(You will lose all the clients at site B). Then you can reestablish communication between clients at site B, and site B sepm, using Sylink replacer.
Then you can use MSL, to have all your clients report to site B. Then you can uninstall site A.
But, first, you need to ensure that both site A , and site B, are at Mr4.
Vishal.