– Click the picture that you want to change the brightness for.

– Under Picture Tools, on the Format tab, in the Adjust group, click Corrections.

If you do not see the Format or Picture Tools tabs, make sure that you have selected a picture. You may have to double-click the picture to select it and open the Format tab.

– Under Brightness and Contrast, click the thumbnail that you want.

 You can move your mouse pointer over any of the thumbnails, and use Live Preview to see what your picture will look like before you click the one that you want.

– To fine tune the amount of brightness, click Picture Corrections Options, and then under Brightness and Contrast, move the Brightness slider, or enter a number in the box next to the slider.

 If you are using PowerPoint, you can still save the original version of the picture, even though you have changed the brightness of your picture. This feature is not available in Word or Excel.

Via: Microsoft