Images you want to add on your shop will not get in the right size automatically. Therefore, it is critical to put your image in the right size before adding it to your shop. The sizes for each of the image types are shown below:
Logo → 150 x 150
Banner → 1920 x 800
Blog Posts → 370 x 253
The second thing you need to make sure is that your image is in the right format before adding it to your admin. The image formats which will need to be used are PNG and JPJ image files.
Tip when uploading images
When you upload images avoid using the same name for the images. When different images have the same name, only one or none of the images will be uploaded to your shop.