I have seen in videos of Windows Phone 8.1 that some homescreens have 3 medium tiles in one row or 6 small tiles. My screen only has 2 medium tiles to a row or 4 small tiles and as I have a lot of applications I'm just wondering how this is accomplished.
It's very simple, just go to Settings → Start + theme and enable the "Show more tiles" option. This enables two extra small tiles or one extra medium tile per row.
For more information, see these links: