Changing the name of OS [in boot menu only] is beneficial when there are multiple OS installed, so they can be easily identified...
To change follow -

1) Open Command Prompt.
[Press Windows Button + R, a window will prompt, then type cmd in text box and click OK]

2) Now type "bcdedit" [Without quotes] and press Enter.




3) Now you can see the name of OS as shown in above figure.

4) To change the name type "bcdedit /set {current} Description "NAME YOU WANT"".
[Replace "NAME YOU WANT" [With Quotes] with any OS name you want]

for example -
"bcdedit /set {current} Description "Windows PHOENiX" and press enter key.

5) Then you will be notified that process was successful.
Enjoy...