Since you've manually installed the agents, you won't be able to push UR6 from the console. You'll have to manually install UR6 on each of the agents.
Unless...you want to pull a not-authorized trick in SCOM. In the OperationsManager DB is a table called MT_HealthService and a column called "IsManuallyInstalled". When this column =1, that means that agent was Manually Installed. If it's set to
0, SCOM thinks that the agent was pushed from the console. You could go to the DB and set this column to 0 for all of your agents, then you can push the UR from the console to all agents. We have a nightly job on our DB server that sets this to 0 for all agents:
begin tran
update MT_HealthService set IsManuallyInstalled= 0
where IsManuallyInstalled = 1
commit
Note that this is not MS approved, but we've been doing this at my shop since we deployed SCOM2007 many years ago and it's worked great.