If you current have an app that tells the UFs where to find the DS then all you need to do is update that app with the new DS's address. Each UF will update itself and contact the new DS.
Since you are asking this question, I'll assume you do not have such an app today. You probably have $SPLUNK_HOME/etc/system/local/deploymentclient.conf on each UF. This practice is strongly (perhaps not strongly enough) discouraged for exactly this reason.
Create your app. Call it something like 'org_all_deploymentclient' and push it to all UFs.
Then comes the hard part. You need to delete the $SPLUNK_HOME/etc/system/local/deploymentclient.conf file from every UF. Let's hope you have a centralized way to do that (Puppet, Chef, etc.), otherwise you will have to log in to each UF to delete the file.
--- If this reply helps you, Karma would be appreciated.