Choose Image > Image Size.
The Image Size command in Photoshop includes a method to preserve details and provide better sharpness while enlarging images.
In addition, the Photoshop Image Size dialog box has been updated for ease of use:
Choose Image > Image Size.
Do any of the following to modify the image preview:
To change the unit of measurement for the pixel dimension, click the triangle next to Dimensions and choose from the menu.
To maintain the original ratio of width to height measurement, make sure that the Constrain Proportions option is enabled. If you want to scale the width and height independently of each other, click the Constrain Proportions icon to unlink them.
You can change the unit of measurement for width and height by choosing from the menus to the right of the Width and Height text boxes.
Do any of the following:
(Optional) From the Fit To menu:
Enter values for Width and Height. To enter values in a different unit of measurement, choose from the menus next to the Width and Height text boxes.
The new image file size appears at the top of the Image Size dialog box, with the old file size in parentheses.
To change the Resolution, enter a new value. (Optional) You can also choose a different unit of measurement.
If your image has layers with styles applied to them, select Scale Styles from the gear icon to scale the effects in the resized image. This option is available only if you selected the Constrain Proportions option.
When you finish setting options, click OK.
To restore the initial values displayed in the Image Size dialog box, either choose Original Size from the Fit To menu, or hold down Alt (Windows) or Option (Mac OS), and click Reset.
Photoshop chooses the resampling method based on the document type and whether the document is scaling up or down.
Preserve Details (enlargement)
When this method is chosen, a Noise reduction slider becomes available for smoothing out noise as you upscale the image.
Bicubic Smoother (enlargement)
A good method for enlarging images based on Bicubic interpolation but designed to produce smoother results.
Bicubic Sharper (reduction)
A good method for reducing the size of an image based on Bicubic interpolation with enhanced sharpening. This method maintains the detail in a resampled image. If Bicubic Sharper oversharpens some areas of an image, try using Bicubic.
Bicubic (smoother gradients)
A slower but more precise method based on an examination of the values of surrounding pixels. Using more complex calculations, Bicubic produces smoother tonal gradations than Nearest Neighbor or Bilinear.
Nearest Neighbor (hard edges)
A fast but less precise method that replicates the pixels in an image. This method preserves hard edges and produces a smaller file in illustrations containing edges that are not anti-aliased. However, this method can produce jagged effects, which become apparent when you distort or scale an image or perform multiple manipulations on a selection.
A method that adds pixels by averaging the color values of surrounding pixels. It produces medium-quality results.