You need at least version 5.2 in order to have tethered support for the D7100. There is no support for tethering for that camera in Lightroom 4.
Thank you so much JimHess :-)
So if I already have the version 4, can I just download the newest version (cause I have seen updates on Adobe‘s website)? Or I need to buy a newer version? Sorry, but I am just a bit confused how this really works. Thank you once again!!
Lightroom 5 will be a paid upgrade for you. Here in the US that upgrade costs $79 when purchased from Adobe. I don't know what it will be for you. The upgrade can be installed in addition to your Lightroom 4. Or, if you prefer, you can uninstall Lightroom 4 and then install the new version. In either case, installation of the upgrade depends on both your Lightroom 4 serial number as well as the serial number for your new Lightroom 5.
After you install Lightroom 5 it will create an updated copy of your Lightroom 4 catalog. The transition is relatively simple. After you are certain that you no longer need Lightroom 4, it can be removed from your computer. But be sure to store the serial number in a secure place.