resize an image in a single layer in photoshop
Use the 'Free Transform' command. Check the chainlink between the height and width field to maintain aspect ratio.
Select the layer you want to resize and go to Edit, Transform, Scale to get the handles to resize the layer. You can hold the shift key to constrain it so the bird doesn't get warped. Just drag a corner until it's the size you want, select the move tool to move it back if the resize put it out of place and your are done.
Ctrl+T Transformers the layer that is selected.
You can transform the layer to fit