Hello
I do not want to do a fresh installation of SAP ERP6 but install it on existing NW7.4
This is not possible as EHP7 for ERP 6.0 is part of SAP Business Suite 7i 2013. When you started the installation you should have installed ERP 6.0 EHP7 under SAP Business Suite 7i 2013. If you want to upgrade an existing system to EHP7 then the system should be ERP 6.0.
Reagan