Hello Din Islam;

You cannot run a newer version of WinCC with a previous version license. You WinCC v7 Licenses will not work with either WinCC v7.4 or v7.5 versons.

Upgrade licenses will be less costly then full licenses. You will need to locate the licenses you need and find the corresponding upgrade license for your application in the Siemens catalog.

I suggest you open the ALM (Automation License Manager) and take note of the existing types and part number of WinCC licenses you have at this time, RC, RT and the number of tags associated with each. Then open the Industry Mall ( Siemens electronic catalog on the web, link below), look in the Navigation tree at the left of the screen, open Automation Systems, HMI Software, WinCC v7.  Once you are looking at the WinCC v7 Baisc packages, add a filter by Package (at the right of the screen) to search only for upgrades, this will reduce the number of packages offered and make your search easier. 

https://mall.industry.siemens.com/mall/en/ca/Catalog/Products/10042373?tree=CatalogTree

Finally look for the upgrade packages that match your existing licenses and the version you want to upgrade to.

Another (simpler) way would be to contact your local Siemens rep with your list of existing licenses from ALM and ask him to find the appropriate upgrade licenses you need... He can also provide pricing and delivery times.

Hope this helps,

Daniel Chartier