Hi,
The term Version upgrade refers to the upgrade of SAP release. An upgrade from SAP R/3 4.6C to ERP 6.0 is a Version upgrade.
Enhancement Package upgrade is moving from one enhancement package release to another for an SAP solution.
For example EHP upgrade from SAP ERP 6.0 EHP3 to ERP 6.0 EHP5.
Thanks
Rishi Abrol