By Attributes

Step 1 - Be sure that you have enabled these options: (From Theme Options → Variation Swatches)

Step 2 - Go to Products → Attributes then create the variation in the brand and change the swatch type into Custom Image. Then, you must provide an image for each Variation by clicking Edit each Variation and uploading its image.

You will then get a result like this

Step 3 - Next, please add custom attributes on the Single Product

Step 4 - Final, navigate to Theme Options → Product Brands and enable this feature