You may reduce the picture size by “Compress Pictures”.

  1. Select the picture need to be compressed.
  2. Under “Picture Tools”, on the “Format” tab, in the “Adjust” group, click “Compress Pictures”.
  3. To compress the selected pictures only and not all of the pictures in the document, please select the “Apply only to this picture” check box.
  4. Under “Target output”, select the resolution that you want.