To change the dots per inch on a JPEG file in Microsoft Picture Manager, highlight the image. Go to the toolbar, select the picture pull-down menu, open the resize window by clicking on the Resize tab, and choose the desired option for resizing the image. Look on the bottom of the resize window at the size setting summary, and confirm that the new size is different from the original size.
Once the correct size has been confirmed, click on Okay. The new size is not in effect until the image is saved. Go to the disk icon located on the toolbar, and click on it to save the image. In order to save a copy of both the old size and the new size, go to the File menu on the toolbar. Click on Save As. In the window that pops up, give the resized image a new file name. Click Save. A JPEG image may also be resized using Microsoft Picture Manager's export function. This option is located on the File toolbar menu.
Changing the dots per inch on a JPEG image alters the size and the resolution of the image. Doing this effects how clearly or detailed the image appears on a printed page.