Hi,
As you are already at EHP6 you need to go in Solution manager and have to selected the usage type for HR in MOPZ while downloading the packages.
In this you will get HR at 604 but you will have to check about EA-HR also as these are patches for the HR functionality.
EA-HR will have other dependencies.
So please generate the stack.xml file for this upgrade.
Thanks
Rishi Abrol