The last free Update for 5.00.6 is 5.03.1, you'll get it at the support page simwerk.de, "klick me".
"Reflex XTR 5.03 für Windows® Vista® (Englisch)" is for XP and Win 7 also, the installer has a problem with Win 7 it will not copy the reflex.exe. So install it on XP or Vista and copy the reflex.exe.
The 5.04 version is not running with your dongle, but there are 2 new sceneries and one heli to copy...
The newest version is 5.06.2, you have to pay for the "hardware upgrade" with sending back your old dongle, to get the new one.
Pleas send mail to simwerk and ask for informations.