To edit the default image banner on your homepage when you install your shop, you need to configure the Banner module.
To make your changes, click on the Modules menu, then on Modules and Services. Then click on the Installed Modules tab. To easily find the Banner module, just enter the word 'banner' in the search field and confirm to show the modules that meet the criteria entered, so the Banner module.
Once the module is displayed on the screen, click on the configure button to the right of your module to open the configuration window.
You can then download the image you want, define the URL of the page where the customer or visitor will be taken when they click on the banner and lastly enter a description for the banner.