When replacing pictures, here are a few helpful notes on sizes that work well for areas of the template.
(1) Header Image – rectangular (tall) image works best to retain the placement of other items on the page.
(2) Gallery Images – these images can be any shape that suits your needs. You will find that it works best to have all images that are similar in shape and size to retain the consistency & shape of the slider.
(3) Background Contact Image – almost any image (shape/size) will work here. A larger image (at least 1000px wide) will offer the best quality when it is stretched on bigger screens.