I have not connect ec2 instance by instance and ssh key

I have changed instance type . Afteward I can't connect my new instance by instance and ssh . I have created new key pairs but it did not help me. If connect by instance . I have occured by this error ."There was a problem connecting to your instance Log in failed. If this instance has just started up, wait a few minutes and try again. Otherwise, ensure the instance is running on an AMI that supports EC2 Instance Connect."