How do I make my terrain larger?

Set the Terrain Width/Length/Height values to bigger numbers than they currently are…

Seriously, did you even try looking in the manual?

+1 was getting links to duplicate questions : * http://answers.unity3d.com/questions/499081/no-option-to-create-terrain.html * http://answers.unity3d.com/questions/502477/why-dont-i-have-a-terrain-button-in-the-settings-t.html * http://answers.unity3d.com/questions/462647/why-can-not-i-do-terrain-unity3d-in-the-new-versio.html

Yes, I looked in the manual. I also had tried that already and it didn't work. I wasn't just asking some stupid question or anything. I tried again later and it worked, though.