Things You'll Need
Instructions
 
Enlarge a Photo in Photoshop
 
Open the photo in your Photoshop program. 
Click the Image drop-down menu and select "Image Size." 
Select "Constrain Proportions" once the Image dialogue box opens. 
Adjust the width or height in either pixels or inches. 
Click "OK." 
Enlarge a Photo in Windows Live Photo Gallery
 
Click on the photo you want to resize in Windows Live Photo Gallery. 
Open the File drop-down menu. 
Select "Resize." 
Select a new size for the photo in the Resize dialogue box. 
Click the "Resize" and "Save" button. 
Enlarge a Photo in iPhoto
 
Open iPhoto program and select the desired photo while in "Organize" view. 
Open the "Share" drop-down menu and click "Export" for iPhoto 5, or open the "File" drop-down menu and click "Export" in iPhoto 4 and 6. 
Select "Scale" in the Export Photos box. 
Enter your desired size in pixels. 
Click "Export."