The Brightness/Contrast adjustment lets you make simple adjustments to the tonal range of an image. Moving the brightness slider to the right increases tonal values and expands image highlights, to the left decreases values and expands shadows. The contrast slider expands or shrinks the overall range of tonal values in the image.
In normal mode, Brightness/Contrast applies proportionate (nonlinear) adjustments to the image layer, as with Levels and Curves adjustments. When Use Legacy is selected, Brightness/Contrast simply shifts all pixel values higher or lower when adjusting brightness. Since this can cause clipping or loss of image detail in highlight or shadow areas, using Brightness/Contrast in Legacy mode is not recommended for photographic images (but can be useful for editing masks or scientific imagery).
Use Legacy is automatically selected when editing Brightness/Contrast adjustment layers created with previous versions of Photoshop.
Click the Brightness/Contrast icon in the Adjustments panel.
Choose Layer > New Adjustment Layer > Brightness/Contrast. Click OK in the New Layer dialog box.
You can also choose Image > Adjustments > Brightness/Contrast. But keep in mind that this method makes direct adjustments to the image layer and discards image information.