Adjust tonal range with Curves layer

On the Photoshop on the web homepage, under Start something new, select Upload an image and browse for a file on your device.  

Select Adjust  >  Curves.

In the Properties panel, select from the available Curves modes: Points or Draw. 

In the Properties panel, select anywhere on the straight diagonal line in the histogram to add nodes. As you add nodes to the diagonal line and move them, the shape of the diagonal changes into curves, reflecting your adjustments.

• Moving a node toward the top portion of the curve adjusts the highlights. Moving a node in the center of the curve adjusts the mid-tones, and moving a node in the bottom section of the curve adjusts the shadows.
• Moving a node near the top of the curve downward darkens the highlights. Moving a node near the bottom of the curve upward lightens the shadows.
• Moving a node either down or toward the right maps the input value to a lower output value, and your composite darkens. Moving a node either up or to the left maps a lower input value to a higher output value, and the composite lightens. Instead of adding a node, you can manually enter an input value and required output value for more specific adjustments.
  

Select to delete a node at any time.

Select Reset  to reset the curve and remove applied adjustments. 

Select Download.