This will update the current model (the "New" model) with Space Attribute and Template data by matching spaces to an existing model (the "Old" model).
The following window is popped-up -
Initially this shows the list of spaces in the "New" model - the assigned templates are shown when spaces are selected, and can be modified by clicking the "Apply changes to Space" button. This dialog can be used to check and update the model without going into the full "Model Merge".
The next step is to select a "Merge Spaces By" option, if you haven't made a selection and click the "Browse" button first you will be prompted to do so.
When you use the "Browse" button to select the "Old" model, you will get the following pop-up warning -
When you have selected the "Old" model it replaces any templates you have in your "New" model and replaces the assignments to spaces it has "matched" between the two models. The dialog is updated to show this -
Spaces that have failed to find a match will show "<no match>" and these can be updated by selecting a space from the "Old" model and using the "Copy to New Model" button.
Rendering
Use this option to toggle between basic / intermediate / advanced rendering. This gives you the option to allocate more memory to the rendering process, resulting in a smoother user experience.