How to Resize An Image in Photoshop?

Step1:
Open the document in Photoshop.

Step2:
Go to Image > Image Size…
A box will appear:
Reduce the Resolution to 72 pixel/inch.

Step3:
Now Go to Image > Canvas Size…
A box will appear:
Adjust the Width and Height according to your requirement. Adjust the Image to make it vertically and horizontally centers align.

Step4:
And finally save the image (Ctrl+S) as a .jpg or .gif format.