From Admin panel, go to MGS -> MGS Theme Settings -> Catalog set Enable Hover Change Image to Yes
From Admin panel, go to PRODUCTS → Catalog → [Edit Product]
On Edit Product page, go to Images And Videos section, Upload image for product.
After images uploaded, click image to set image role: base image, small image, swatch image, thumbnail image.
For first image show, it is small image. For image product show when hover item, it is thumbnail image and base image.
Save product.