This dialog is available from the File / File Operations / Scale Prices... menu command.
This command will scale all your price information for all investments in the specified portfolio. You specify the date range to perform the scale, and the multiplication factor. All price information (close, open, high, low, and transaction prices) in your investments will be multiplied by this multiplication factor. The scaling dates are inclusive, that is if there are prices recorded for the specified dates, these will also be scaled.
This command may be useful in certain situations, such as if your investments change currency. If you have been tracking investments in one currency, and then they switch to a new currency (for example, the Euro) your prices all need to be scaled, but the number of shares should stay constant.