Use the Smooth command to smooth the edges of a selection.
To smooth the boundary of a selection:
Choose Selections > Modify > Smooth to open the Smooth Selection dialog.
For Smoothing amount enter a number for the level of smoothing for the corners of the selection.
Note: In the dialog you can click the Toggle Selection button to change between showing only the selection or showing the selection and the rest of the image.
For Corner scale enter the number of pixels at the corners of the selection to smooth.
Anti-alias mark this check box to smooth the edges of the selection.
Preserve Corners mark this check box if you want the corners preserved. Clear this check box if you want the corners to be smoothed.
Click OK. The selection is smoothed.
Adding or Removing a Color from a Selection
Changing the Feathering of a Selection
Cleaning up the Edges of a Selection
Modifying the Select Selection Borders