How to delete Instances in Amazon EC2 ? Change Pair Key?

How to remove Instances ? I test some Instances and now I terminate it. So, I want to remove it. I can't find delete or remove action. I just found terminate.

How to change the pair key ? I don't have pair key for old Instances and I want to configure that instances.

If your instance uses the instance store as its root device (e.g. it's not an EBS backed instance), simply terminating it will destroy the instance and you won't have to do anything else.

Give it some time. Deletion of terminated instances is not a high priority task within the EC2 stack (seems reasonable to me). Eventually the terminated instance will drop out of the interface.