How can you convert your iPhone pictures to jpg?

Photoshop

If you took the picture with your camera lens, it should already be a a .jpg upon being transferred to your computer.

You can also open the pictures in an image editing program such as Paint or Photoshop, then re-save them (Save-As) .jpg. There is absolutely no need to use websites or download anything in order to convert images to .jpg, these downloads are usually spammy, malware or malicious.