How to transform a Player into another Humanoid Model in the place itself?

I want to know how to do this so. On my character chooser GUI. When someone presses a certain character image button their character will transform into that character before they press play. Thank you really much!

You could have a morph right, of the character there going to pick. And when they hover over the character a button script will be there and you can connect the button so that when they press it. It will turn them into the morph off screen.