login - How to shift user in ubuntu using ssh keypair - Ask Ubuntu

in aws ec2, login ubuntu user ssh keypair:

ssh ubuntu@hostname -i path_to_the_keypair 

now, want shift root user try login root user entering

$ su root 

and asks password how enter ssh password.

is there way change user using ssh keypair?

no. can't authenticate su using keypair. have configured sudo , can "change root user" using sudo -i.