ImageResize

ImageResize[image, width] gives a resized version of image that is width pixels wide.

ImageResize[image, {width, height}] resizes to exact dimensions.

Examples

Resize by width:

img = ExampleData[{"TestImage", "Lena"}];
ImageResize[img, 256]

Resize to exact dimensions:

ImageResize[img, {200, 300}]

Please visit the official Wolfram Language Reference for more details.