HELP - Change DPI so that I can make 8x10 prints of pictures ASAP!!!?

I have a few pictures from the internet saved on my computer. I took them to Target on a disk to get a few 8x10's printed and they said they were blurry and that I need to change the DPI



PLEASE help ASAP what software or how-to do this fast!



MANY MANY THANKS IN ADVANCE:)HELP - Change DPI so that I can make 8x10 prints of pictures ASAP!!!?
the pictures you have downloaded are a very low dpi and you will find it impossible to get a good result at that size download it as a bigger file say 4 mb or more , this will allow you to print at a4 sizeHELP - Change DPI so that I can make 8x10 prints of pictures ASAP!!!?
You may use any professional picture editor such as Adobe Photoshop or Corel PhotoPaint, or other good editors such as GIMP, to enlarge de size (in pixels) of the photo as to match the size of photos taken by digital cameras, such as 1600x1200 (2 megapixels), 2048x1536 (3MP), 2272x1704 (4MP), 2560x1920 (5MP), 2816x1944 (6MP). These programs have also options that will allow you to smooth the edges and shapes, enhance colors and contrast and other useful functions to make the photo look better when upsized from a small original size. Then you'll be able to print it correctly. Hope that helps...
Your pictures may have a very low resolution, that's why usually prints look awful. So, check the resolution of your pictures. If don't know how to, just look at the size of the picture: 800kB for a 8x10 print is acceptable, hovewer a picture of 20kB won't look gorgeous.
Your actual source files need to have higher dpi--you can't just change the existing files as you can't add in information to the file. You could liken your existing file to a glass of water--the information in your file being the water and the glass being your dpi. If you pour the water into a large pitcher, you still have the same amount of information trying to fill up all of that dpi that is the pitcher. Sorry!