To replace an image with the new one in the Slide View editor:
  1. Right click an image and select the Change Picture command
  2. Locate a new picture in the Open window.
  3. Click Open.

The new image will replace the existing one. With this method, you have the benefit of retaining the image position and size.  

You can apply the same action to an equation. The Change option opens the Microsoft Equation Editor where you can edit an existing equation.