You can register a public key during the creation of your instance for SSH key authentication during SFTP and Git access. Please note that this is not available for SSH console connection.
To do this:
ssh-keygen -t rsa -b 2048
1. Login to your instance via SFTP
2. Navigate to the folder named '.ssh' located at the root of your SFTP directory listing
3. To remove all SSH public keys simply delete the file 'authorized_keys'. Alternatively, you can edit the file and remove only the SSH public keys that you wish.