How to allow textbox to save text after finish typing

Question

Hi guys i have problem i write update statment in textchanged event.but repeated changed when any charachter changed

example

user name text box and has name ahmed and i need to change to ahmedsalah

it save in database as

ahmeds

ahmedsa

ahmedsal

ahmedsala

ahmedsalah

it save 5 times

how please to allow textbox to save after finish typing 

I have sql 2005

visual studio 2008

if possible help me