just generate a new password with a register script and paste the hashed results into your account table this will change your password in the game...
however it appears that you are trying to creat a mysql user in which case it is not part of the account table but in the mysql db user table
the easiest way to edit this for someone who doesnt know how is with navicat and you can do this by simply connecting to your db with the root account and selecting users up near the connection tab... if I am mistaken or you need clarication just say