How can you change the username in Microsoft Office applications such as Ms word, ms Excel,...etc?

from the file tab then options at general change the username

In Excel2013 ............. Go on File; Options, then in middle it gives options to change user!!

The same would be for Word and PowerPoint.

This feature may come with MS Office360, right ?

I AGRRE WITH MR AHMED MAHR ANSWER  

In Office2013 - File > Options > Office Account > make edit to user if you are signed in by MS account. 

Locally can be changed - File > Options > General > Personalize your copy ... and change username.