How do we change instance type? At what state instance doesn't allow us to change type?

What are the payment options and which is less chargeable one for 1 year?

Difference between On demand and reserved instance?

What are pricing models?

how to confirm internet reached to Amazon virtual machine and describe what are the status check involved?

AWS checks the virtual machine itself—network configuration, OS boot, and reachable network interfaces. If this fails, the issue is inside your instance (firewall, OS, drivers).