I have moved your post into the Data Protection \ Encryption: ePO Managed forum for better visibility.
You can't run two ePO agents on a client- only one, so you would have to use the existing ePO.
You would need to check of course the options for upgrading- if your current version is supported to upgrade to v6 and if all the features your require are available in v6.
There are a few features that others have mentioned do not exist in v6 that are in v5, so you'd need to check that.
Here's a good faq with the lonk to the guide on how to upgrade: https://community.mcafee.com/community/business/data/blog/2010/11/11/faq-upgradi ng-from-eepc-v5-to-v61
As Jane said, you can't upgrade v5>v6 - you can migrate v5>v6 though.
So, you'd install the EEPC6 extensions into your existing EPO server, then migrate your clients over as needed.
Once they are all moved across and you're seeing zero traffic on your EEPC5 environment, you can decomission it. I'd keep a backup just in case you find a laptop in a drawer in the future.