I'm new to photoshop cc and I'm trying to cut and paste a picture of a person from one photo to fit in with other people in a different photo. They're two different files but when I copy the picture from the first file and paste it to the second one the first one is so much bigger than the second. How do I fix this?
First instead of pasting, use the File > Place command to put the image you want to change onto the target image.
Use the handles on the placed image to scale, rotate and move it down to where you want it.
Then press enter to commit your transformed image. It will be on a separate layer, so you can come back to it later for further adjustments using the Edit > Free Transform command.