If it is the latter, then you have to upgrade your STEP7 version. I think the ability to update the HW catalog came with v5.3. The current version is v5.4
The Hardware Support Packages enable you to configure modules that are not included in the Hardware Catalog of your STEP 7 installation.
As from STEP 7 V5.2 onwards, you can use the Hardware Support Packages to update your existing Hardware Catalog.