How do I upgrade Ubuntu desktop to Ubuntu Server?

Related questions

1. What is a Ubuntu server?
2. Why is Linux good for servers?
3. What is sudo apt get upgrade?
4. Does updating Ubuntu delete files?
5. How do I find system information in Ubuntu?
6. Which Linux is used for servers?
7. What's the difference between Ubuntu desktop and server?

Tags

1. #upgrade
2. #command
3. #ubuntu
4. #window
5. #installed
6. #first
7. #headless
8. #server
9. #preferred
10. #package
11. #using
12. #update
13. #terminal
14. #software
15. #existing
16. #configuration
17. #desktop
18. #manager
19. #editor
20. #following