Done this a few times
Log in, click my domains, get the domain on the screen, tick the checkbox. You will see a set of images towards the top of the screen, but a little lower. .. three rows wide, two or three rows of images (options) long.
First row, in the middle, image reads: change ownership
click that
Then enter the new registrants details in the fields that show up on the right.
You will need their name, address, phone number, and email.
They get an email.
They log in, click my domains, then on dropdown menu at that screen, they choose "accept an account change"
They enter the two codes they got in their email - transaction ID, and security key.
.. and viola. Domain changes hands.