Or open them in "Paint" (everyone has a copy of that, right?)and in the "Image" option select "Stretch/Skew" and enter the % for BOTH horizontal and vertical that you want to shrink it by (obviously 50% would make then half size) OR in the "Image" option selct "Attributes" and enter the width/height in whatever "Units" you need, then "Save As" a copy of the original without amending the original
