Hi Chris,
VisualDSP++ 5.1 can be downloaded from the VisualDSP++ Product Page at the following location:
www.analog.com/visualDSP
Click on the, 'Download VisualDSP++ free 90 day evaluation software' (release 5.1.0) link. This is the FULL version, not a 90 day version as the title suggests. The file is a *.exe file and not a *.vdu file as VisualDSP++ 5.1 is separate to VisualDSP++ 5.0 and will be installed alongside your existing version of the tools.
Note, when installing 5.1 you have the option to copy over the license from your existing version. To do this click on 'Advanced' when the installer asks for the installation path and check the box to enable copying over a license.
Regards,
Colin.