Resize JPG files by using an image editor such as Adobe Photoshop or a website application such as ImageResize.org. While the website is free to use, Photoshop costs money.
To resize a JPG file using Photoshop, open the application and drag the JPG file into the Photoshop window. Click Image on the menu bar at the top and select Image Size from the list. Once the Image Size dialog opens, indicate a new size and click OK. Alternatively, you can press Option+Command+I on Mac OS X systems or Alt+Control+I on Windows computers.
If you already have another image open in Photoshop, make sure you drag the JPG file into the toolbar at the top. Dragging it into an open image causes Photoshop to add the JPG file on top of the open image as a new layer.
To use ImageResize.org, click Browse on the home page, navigate to the folder that has the JPG file, open the file and click Upload. Once the JPG file uploads, select a new size from the drop-down menu, make sure JPG is selected at the bottom, and click Process Image. Right-click on the resized image and select Save Image As to save it to your computer.
Because the JPG file format stores image information as pixel data, scaling up the file results in blurriness. Likewise, scaling it down causes some details to disappear. It is not possible to restore lost details by scaling the image up again.