Upload store logo
From Shopnix Help
Your store logo represents your brand. You might want to get it designed by professional logo designers.
Note: If you are using our standard themes, ensure that you provide the designer with the expected image dimensions for these themes - 300pixels wide x 100pixels high. If you getting a custom theme designed, your logos can be of any size.
Once you have the logo ready, you can upload it in the 
section. All you need to do is, click on the Choose file button next to the logo section, select the logo image from your computer and click Save. The image will be uploaded to your store and applied automatically.