There are a number of sections that can be edited on the homepage.
The Featured Links section can be edited by navigating to Content > Link Lists > "Featured Links". This section can accept 1, 2, 3, or 4 links with images It is recommended that image sizes all be the same. Reccomended image sizes are as follows:
4 Images: 220px by 131px
3 Images: 300px by 182px
2 Images: 461px wide, no more than 276px tall
1 Image: 942px wide, no more than 276px tall