changing username

How can i change my username in ubuntu?
I tried
usermod -l newname oldname

but it is saying that
usermod: user oldname is currently logged in

anyone help me

change user name

Is this any help? I just typed the title into Ubuntu's search box...!

http://search.ubuntu.com/results2.html?cx=009650792990864903260%3A-lsdjs...

I did not get u. can you

I did not get u.
can you explain it in detail.