In case of installation, re-installation or any other OS related issues, the machine name has to be provided.The name is actually used to distinguish that computer from others when placed in a network. 

The computer name must be unique when your device is part of a network. Otherwise, there will be conflicts between two or more computers with the same name. When that happens, others are not able to access them and their shared resources correctly.

The computer name can be anything you want. But you are restricted when it comes to its length and the characters that are allowed as part of the computer name. The computer name must have up to 15 characters. Also, you cannot use the following characters: /\ [ ] " : ; | + = , ? * _ (caret, square brackets, quotation marks, colon, semicolon, pipe, less-than, greater-than, plus, equals, comma, question mark, underscore and space).

Pre-requisites

1. Windows OS -
   

   Windows Server 2008 R2 SP1

   Windows Server 2012 

   Windows Server 2012 R2
   
   

2. Log in with Administrator credentials.

Step-by-step guide

For Windows Server 2008 R2 SP1

1. Open the Control Panel and choose System and Security.
2. Then, click the System category.
3. In the System window, scroll down to the Computer name, domain, and workgroup settings section.
4. There, click Change Settings.
5. The Computer Name tab will be selected in the System Properties window. At the bottom of that window you'll see: To rename this computer or change its domain or workgroup, click Change. Click the Change button.
6. This pops up the Computer Name/Domain Changes window. You will see your current Computer Name and the current Workgroup.
7. Change it to anything you want, keeping in mind that there are some characters that are not allowed in computer names. Microsoft lists those characters as: /\ [ ] " : ; | + = , ? * _ (caret, square brackets, quotation marks, colon, semicolon, pipe, less-than, greater-than, plus, equals, comma, question mark, underscore and space). If you try to use one of those forbidden characters, your name change won't go through.
8. Click OK and you are informed that you must restart your computer to apply the change. Click OK again.
9. In the System Properties window, click Close.
10. Your name change won't take effect until you restart the computer. You'll be asked if you want to restart. If you don't want to do that right away, you can choose Restart Later. Otherwise, make sure that you do not have any opened documents or apps and choose Restart Now.
    
    

For Windows Server 2012 and  Windows Server 2012 R2

1. Go to Server Manager > Local Server.
2. Click on Computer Name.
3. The Computer Name tab will be selected in the System Properties window. At the bottom of that window you'll see: To rename this computer or change its domain or workgroup, click Change. Click the Change button.
4. This pops up the Computer Name/Domain Changes window. You will see your current Computer Name and the current Workgroup.
5. Change it to anything you want, keeping in mind that there are some characters that are not allowed in computer names. Microsoft lists those characters as: /\ [ ] " : ; | + = , ? * _ (caret, square brackets, quotation marks, colon, semicolon, pipe, less-than, greater-than, plus, equals, comma, question mark, underscore and space). If you try to use one of those forbidden characters, your name change won't go through.
6. Click OK and you are informed that you must restart your computer to apply the change. Click OK again.
7. In the System Properties window, click Close.
8. Your name change won't take effect until you restart the computer. You'll be asked if you want to restart. If you don't want to do that right away, you can choose Restart Later. Otherwise, make sure that you do not have any opened documents or apps and choose Restart Now.