To suggest a website or to request for an update you do not need a DMOZ username.
To update a listing go to the category in which teh website is listed.
When you hover your mouse over the listing you will see a flag at the right side of the screen.
It says "report an issue with this listing"
click that flag and tell us what should be changed and why
an editor will look at the request and check teh website to see if the request is valid