Hi Eranga,
VisualDSP++ 5.1 is the latest update for the 5.x tools (though it installs discretely, rather than being installed as an update), and is free for any licensed VisualDSP++ user. You can use the "Advanced" options during installation to copy the license.dat file from your existing installation into this new install, or you can manually copy the license.dat file from the ".\System" folder of your existing installation to the new one.
All of our EZ-KITs come with the VisualDSP++ 5.0 base release on CD, and the installer offers to check for updates at the end of the installation. We have since changed our distribution (though obviously there are a lot of products out there that shipped before these changes) to include instructions on where to download the latest tools, rather than including a CD that may well be out of date by the time an EZ-KIT ships.
Apologies for the inconvenience - let me know if you have any issues with the installation of VisualDSP++ 5.1.
Regards,
Craig.