Not sure that this goes here but question about making fixing pictures

open it with paint and skew it larger

good luck

If you have MS Office then you have "MS Office Picture Manager". Open the file there and under picture menu there is this resize. I would suggest You use the percentage of the original WxH to maintain its proportion. For twice the size use 200%. I would just like to point out the result would be grainy, pixelated or blurred. It would be better to shrink a picture than to enlarge it. But you have no choice, just don't over do it. Finally save it as*.jpg.

It is not really a good idea to expand the size of an image, because as has already been suggested it would reduce the quality quite a bit.
The best option would be to ask your friend to send the images ina larger size. He must have taken decent size images with a digital camera and reduced the size, so if he still has the originals then you could use them. To ensure that they are jpeg simply open them in any photo editor and save them as jpeg. All software has this option and is usually done by clicking on the File button o the toolbar and selecting Save As then Jpeg. If you are not sure what software you have then double click the image to open it and it will select a program itself.

I think adobe photoshop would do the job for you.
Even if you dont want to expand the image to retain the quality you can paste it on a big canvas and then post it.