To sharpen the image choose Filter > Sharpen> Smart Sharpen from the menu.
In the dialog box enter the following: Amount 100%, Radius 1.0.
This usually will sharpen the image enough. If not, try increasing the amount above 100% and a radius of 1.5 to 2. Higher values will be needed for larger file sizes and images with larger dimesions.
Be careful not to oversharpen by entering a radius number that is too high, you will loose color and definition.
