First, you need open the Photoshop software. Then you need import the picture you want to use.
go to crop tool, then you need click on the crop tool, choose 1.5 x 2 ratio.
After that go to edit menu > image size.
With pixel dimensions:
Width 300
Height 400
Document size:
Width : 1.5 inches
Height: 2 inches
Resolution: 200 pixel / inch
You can please see this video for more detail:

