Hi Jenglish,
I’m using version 4.01 and also I didn’t see ‘replace media’ at first.
But I began looking around and I found it!
When you have clicked on a image in your library you see (on the right) three links called (translated from Dutch) “See appendix page – Edit other details – Delete permantly”.
Click on the middle one (Edit other details)
Then you see “replace media”
I hope I helped you with this ??