regenerating thumbnails

I have uploaded the large image of my product at 1024 x 1024 72ppi.

But I cannot make the thumbnail and the medium sized pic the sizes they should be. I have tried regenerating thumbnail and this doesn’t work, so my 2 smaller pictures are poor quality.

How do I get all three to look amazing?

I need the pic in:
1024×1024
300×300
and 150×150