To change you own user name in linux if you have only one account, proceed as follows:
1. create another temporary user, e.g. tempo:
sudo adduser tempo
2. Give him permissions for sudo:
sudo adduser tempo sudo
3. Logoff from you username. Go to TTY5 and login as tempo
4. Suppose your username is john and you want to change to michael.
In there type in as sudo:
usermod -d /home/michael -m -g michael -l michael john
6. login again now as michael, and that’s done.
Logoff from tempo in TTY5 and delete tempo account:
sudo userdel tempo