I have change the username in my macbook and suddenly it seems like I just opened my macbook for the first time as I was prompted to enter all my account details again. And even my files from my old account suddenly gone. I am sharing via video tutorial on how I managed to recover my files from my previous account.
Meanwhile, here's on how to change user account on Macbook
Each user account in OS X has a full name and a short name (account name). You can view these names from the Users & Groups pane of System Preferences, and you can use either name to log in to your Mac.
A user's full name can be changed by that user or an administrator. The full name doesn't need to be the same as the account name or home folder name.