How do you change dpi in Photoshop?

I need to save a project at 350 dpi or greater.How do you change dpi in Photoshop?
you can see the DPI of the image if you go to the menu on top, select Edit / Image Size.



In there you will see the size in inches or centimeters, whatever you haev it set to. Then below that you'll see the DPI, probably 72, 150, 200, 300, etc...that's where you change it.How do you change dpi in Photoshop?
I'm fairly sure that you have to set the dpi when you first create it (although i could be wrong)