For example you can change this basic theme into a Sci-Fi game. In the "Toolbox" you have "Skybox". This option allows you to change how the sky looks. You can also customize the colors and materials of all the parts with just a few simple clicks. You can change stones to metal and add some glowing effects to it. To to this go up to the model tab and select the material and the color you want. Once you get familiar with the options it may take as low as an hour to make something completely different and unique from what you started in the first place. As you learn new skills you can continue to edit the game by adding new obstacles, making custom graphics and even changing the animations. When you are ready to show off you game just click "File" and "Publish to Roblox".
The great thing about these themed games is that you can tinker with them and pull them apart to learn more about the different aspects of Roblox Studio. Try changing properties or looking at the scripts and get started learning about what Roblox Studio can do.