Acrobat is not a graphics tool. The JPegs are generally stored within the PDF container. They can be extracted with "export all Images," typically found in a dcoument processing menu. An alternative is to save the PDF as a JPeg that will save each page to a JPeg. I suspect the export all images is what you want.
Simple way, save the pdf as an image file, convert the size using a image resizing tool in Photoshop (file / save for the web), I use a free program instead, much easier than PS; "Image Resizer for Windows" (google it). Acrobat X is a step back from Acrobat 9 (which is a better program in my view and I use it on my laptop) in some cases. The designer(s) are not users! The regression continues with XI.