Yes, you can modify the store page with your requirements. Please check this following link for discussion – http://wedevs.com/support/topic/store-page-display-in-3-columms/. But keep in mind if you customize increase or decrease amount of product it will affect your theme outlook. Then you have to do style for adjust the outlook.
Thanks for your reply.
I must not have explained myself very well. I don't need to know how to increase or decrease the number of columns, what I wondering is how can I increase the amount of product shown on my store page?
There is currently 10 products showing and I would like to increase this to at least 20 products. No matter how many new products I add to the store only 10 shows up on the store homepage.