The pacing at which all terrain tools work is modifiable via the adjust speed slider. Holding shift while scrolling your mouse wheel will change the size of the area, though you can also use the sliders in the interface or press right bracket to cycle through the sizes and shapes.
Terrain can be raised and lowered in small or large areas, with the shape of circle or square. When you select terrain manipulation, the entire land area highlights with a yellow green that shows where Sims are able to build. From here the interface changes, showing you three options - paint, eraser, and terrain manipulation. You'll find terrain tools on the far right side, near the tree.
