If you want to resize a large photo you have to take the correct precautions to prevent losing too much resolution. Making an image smaller can make it appear blurry if you don't do it right. This can make the picture less clear than it should be.
This is a fairly common issue when resizing images, but with Photoshop there's a solution.
To perform this function you must own at least the CS version of Photoshop. If you don't have this version, you may want to get it as it has far advanced features. Buying the software will get rid of the limitations you may have when editing your pictures.
To make an image smaller go to Image> Image Size> Resample Image. Choose Bicubic Sharper from the resulting menu. This setting will minimize any blur that occurs when resizing the image.
When you want to make an image larger, select Bicubic Smoother.
This process is so effective that I would recommend setting Bicubic Sharper as the default selection when you start the software. You can do this by going to Preferences> General> Image Interpolation. Here you can select Bicubic Sharper as the default.