There are two solutions to your question and, although the methods are slightly different, they will have the same outcome. For ease of communication, I will call your old model 'Model 1' and your new model 'Model 2'.

Note: Please take into consideration that if you have renamed any of the materials in your 3D modeling application, you will need to re-apply the Materials in Lumion on the corresponding surfaces.

Solutions:

1. In Build Mode, select Model 1.

On the top right, you should have a dialogue box with a circular arrow next to your model's thumbnail. Keep the Alt key pressed and click on that button. Now you can load Model 2 and Lumion will automatically update your model and Materials.

2. LiveSync allows you to make changes to your model in SketchUp and view them live in Lumion. It is a very handy tool when you want to experiment with design variations or material palettes. You can follow the instructions below on how to install and use LiveSync for SketchUp.

Please note that if you choose this method at this stage of the project, you may need to save your Material Set and re-apply it once you import Model 2 in Lumion.

Our recommendation is to integrate LiveSync in the early stages of modeling since it offers many design benefits. You can find links with useful instructions below:

• Knowledge Base: Download Lumion LiveSync for SketchUp

• Knowledge Base: How does LiveSync 3 work with existing imported models in Lumion Projects?
  

• Knowledge Base:​ How do you copy, paste, save and load materials in Lumion 10.0 and newer versions?

I hope this answers your question. Please let us know if you still come across any issues.

3. Guide/Procedures:

3.1: Reply is SketchUp specific so amend as can be to the users 3D modeling software.

3.2: If they are using an application that does not have LiveSync then include only part 1.

4. Cause/Background information:

4.1: Reference: Staff Dojo Training