Here’s a quick tip for changing the file extension of many types of images. Let’s say you need for a photo to be a .jpg file or but it’s a bitmap.
Many times, the quickest way to change file type on a Windows computer is to open it in using good old reliable Microsoft Paint.

Click the File tab at the top and choose Save ss from the drop-down menu. You’ll have a choice to save as .PNG, .JPG, .BMP, or .GIF. Click on other formats, to see additional options.

Click in the Save as type field for a drop-down menu of other file types.

Other photo editing programs offer this feature as well. Some programs, like Photoshop Elements offer an even greater variety of options.
I’m missing something! What program are you using when you change file types for a picture?
Microsoft Paint as it says in the article.