How do you change a picture to a jpeg image?

I edited one of my photos with a program called Gimp.

Now it's not a jpeg anymore I guess, and it wont let me upload it to myspace.

How do I change it to jpeg so it will upload?

(The weird thing is, when I open the picture's properties, it says the type of file is JPEG Image. But myspace says that it's not...)How do you change a picture to a jpeg image?
open it using paint. then go to file...save as....and on the bottem drop down box choose jpeg