indd to epub reflow - images display much smaller

I just exported an EPub from InDesign. I had to do a bit of editing since the actual indd is a childrens book with nested images. I did the re edits in Sigil and all I did was move the images  that were nested in the paragraphs of the pdf to in-between the paragraphs. It looks great to me but the client wants the images bigger. Not that much bigger but enough to notice lets say 1 image is 300x250 he wants it to be at least 500.

Is there a way to have the images display bigger from the epub export? all I see is  changing the ppi from 15 to 300 but this does not change the size.

Any help in doing this?

MRD