Hi Teddykan!
From the Help page:
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My drive is filling up. How to move all girls to another drive?
Copy the VGHD data directory from where you have it to the other drive which would then be X:\VGHD (where X is your other drive).
Uninstall VGHD and then reinstall and watch for the option to change the data directory, its not a prompt, just a section on the setup screen.
When you browse to select the drive X, it will display the new destination as X:\\. Do not worry about the second slash. You should then be right to re-update the calendar and the models should not be redownloaded.
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Haven't tried it myself so I don't know if it works...