Resizing and scaling the images ready for printing

I have decided that my portfolio will be an A3 sized box, therefore my images are going to be A3 sized, but my images are out of proportion and not that size yet. Therefore I will have to resize and crop the images, I will also change the DPI (resolution) to 300, this should be a good resolution for A3 prints. 

As you can see, I have changed the document size to an A3 size, but the document itself is too big for an A3 size. I have also change the DPI to 300. To overcome the problem of my document being too big, I will have to crop the image down to the right size.

In the print screen above, you can see that I have set the constraints to the size of an A3 print. This will guide me so I can position the image to how I want it.