Don't bother wasting your dosh on PhotoShop..Trust me the guy that suggested it never bought it either lol
Free Open Source Software
https://www.gimp.org/
N-Joi
Edit:
Oh and i know you love asking questions Alan ...I will read your mind. here is the answer
With GIMP open, go to File > Open and select an image. ...
Go to Image > Scale Image.
A Scale Image dialog box will appear.
To see the Image Size in inches or a value other than pixels, use the drop down beside the values.
Enter new Image Size or Resolution values. ...
Select Interpolation method.
Have fun