Choose Paint Edit > Layer Effect > Sharpen Layer   or choose a brush from Paint > Effect Brush > Sharpen Brush
  or choose a brush from Paint > Effect Brush > Sharpen Brush   and use the brush to sharpen paint.
  and use the brush to sharpen paint.
         
To sharpen all unmasked paint on an image layer
 .
 .
                   ❒ to open the Sharpen Layer Options box
                        and adjust the Sharpness from 0 (no sharpening)
                        to 10 (maximum sharpening). To set the extent that each pixel is
                        sharpened, set the Strength from 0 to 4.
  ❒ to open the Sharpen Layer Options box
                        and adjust the Sharpness from 0 (no sharpening)
                        to 10 (maximum sharpening). To set the extent that each pixel is
                        sharpened, set the Strength from 0 to 4.
                      .
 .
                ❒) and adjust the Sharpness from
                        0 (no sharpening) to 10 (maximum sharpening). To set the extent
                        that each pixel is sharpened, set the Sharpen Strength from
                        0 to 4.
  ❒) and adjust the Sharpness from
                        0 (no sharpening) to 10 (maximum sharpening). To set the extent
                        that each pixel is sharpened, set the Sharpen Strength from
                        0 to 4.