You don’t say if you have the images inserted individually or as a gallery, but you can change the order either way.
If you added each image to the post on it’s own, then you can go into the post/page editor and move the images around. You can do this in the Visual tab by clicking and dragging the images to the order you want them. If you are comfortable with HTML and would rather move them in the code, you can go into in the Text tab you can copy and paste the img lines into the order you want.
If you uploaded the images together and it is a gallery, then in your post/page editor, you’ll want to click on the gallery to open the popup.
