How to set a photoshop image to 300 ppi?

To make changes to an existing document

1.Go to menu Click Image-> Image Size.


2.Uncheck Resample Image

3.Change the Resolution to 300

4.Click ok.
The old document is altered with 300ppi


To create a new document with 300ppi

1.Go to File--> New


2.Change the Resolution to 300
3.Click OK
The new document is created with 300ppi