Photoshop has become an industry standard and is available in many versions such as Photoshop Elements, available at: www.adobe.com.
It’s easy to see the file size of a photo online. Rightclick the mouse over the photo online and click Properties. The type of photo, size and pixel dimensions will be displayed.
To resize a large image in Photoshop
Open the image you want to resize
Go to Image > Image Size
Make sure Constrain Proportions and Resample Image are checked
Under Document Size, set the desired size.(This area is typically measured in inches)
Under Resolution, set the desired resolution (72 pixels/inch is typical for web images)
*Keep in mind that when you change resolution or document size, it will change pixel dimensions, etc. Be aware of the size you are trying to achieve.
Go to File > Save for Web (Save file as a jpg with a Very High setting.)