Use Image->Resize->Image Size to resize the image upward or downward.
Be sure Resample image, Constrain proportions, and Scale styles are checked.
Be sure the resolution is set appropriately for your printer. If not, set it first.
Choose Bicubic smoother in bottom drop-down if you are upsizing.
Choose Bicubic sharper if you are downsizing.
Note that when Constrain proportions is not checked, the image can be distorted, vertically or horizontally.
