How to Control Your Windows 8 Tablet's Touchscreen
Pinch and/or stretch
As a handy way to zoom in or out of a photo, pinch the screen between two fingertips (usually your thumb and index finger). The photo, text, or window shrinks as your fingers move inward. (Lift your fingers when you’ve found the right size.)
To enlarge something, spread your two fingers across the screen. As your fingers spread, the object beneath them grows along with their movements.
Example: Stretch your fingers across hard-to-read items like web pages, photos, and documents until they reach a suitable size or level of detail. Pinch the items to reduce their size and to fit more of them on the screen.