which ePO version do u have ?
have you install the extension for McAfee agent?
try to check in the latest product and create a deployment task to install the MA latest version.
Better you refer Installation guide, it will give you the idea to do Product Check-In..
It's not enought to check-in the product you should try to deploy it over your network.
But i would suggest you first to test the new version on few systems before to deploy it.
I agree with Alex, you should test this version on a few machines before you attempt to install it everywhere.
Within the ePO console, you go to System Tree - My Organization - Client Tasks
There you create a Product Deployment task for the new Agent.
If you want to test it on only a few machines, I suggest you create a new Tag (I usually call mine "Agent Test Tag" or so) and apply this tag to the machines you would like to test this new Agent on. Then create the Client Deployment Task and only send this task to computers with this new tag.