Windows 10 Mobile, like its predecessor, sits somewhere between iOS and Android regarding customization. You cannot just hack and move around everything, but you do have a lot more choice than an iPhone.
One feature that arrived with Windows 10 Mobile is the ability to have more columns on the Start screen. On phones with smaller displays, users can have one wide tile and one medium tile adjacent (or just three medium tiles). On a phone like the Lumia 1520, however, you can have two wide tiles side by side (or four medium tiles).
By default, the Lumia 950 opts for the three-column layout. Personally, I think it is a good choice as it keeps the Live Tiles at just the right size for most users. In Windows 10 Mobile users can also toggle a switch to 'Show more tiles' that adds in a fourth row. Interestingly, this does nothing on the Lumia 950 by default. The reason has to do with text size and is easy to work around.
Without further ado, here is how to enable four column support on the Lumia 950.
Full story from the WindowsCentral blog...