This assumes you have an authorized_keys file from Managing Public Keys for File Transmission Services in your home folder (~) where the SFTP commands are executed.
Any keys not in the file you upload will replace the file on the server, removing them from authorization.
Connected to sftp.onechicago.com.sftp>
Uploading authorized_keys to /.ssh/authorized_keysauthorized_keys 100% 544 92.6KB/s 00:00sftp>
Session closes, No output.