Teach how to change image on websites homepage

I run an e-commerce website selling lingerie and need to change the image that I currently have on the homepage, the current image details "sale", I would like this to be moved to one of the small boxes on the side and replace it with an image of a new line which I can provide. I would also like to add a Valentines messgae in one of the small boxes at the side and link this to the Valentines items that are for sell.