I have a PDF book and the first page is a 2D image of the cover of the book. I have changed the cover of my book so now I need to change the 2D cover image on the first page to match. Somebody else put the book together for me so I don't know how to do that. I know I need to change the image in microsoft word and then save it as a PDF. Can someone tell me how to do this?

I'm using Word 2013, and my image has a little anchor symbol in the bottom left - it says it's anchored to the text at this point. How do I remove this image and replace it with another?