Change the number of featured images on Home Page

Currently the max number of featured images (posts) per page is 10. Because there are 3 columns, when the home page reaches the 10 max images (posts) the Home page appears to have room for 2 more featured images(posts) which makes the Home page looks unfinished/unbalanced/awkward. The max needs to be multiple of 3, i.e. 9, 12, 15, etc. Therefore, when the max images (posts) are reached the home pages looks complete/even/nicer.

How can I change the maximum number of featured images (posts) for the home page?

David H.