[ubuntu-uk] Problem with Username and password for Synaptic

[scoundrel50a]

have tried a couple of times on ubuntu-uk but not got anywhere there, so 
thought I would try here. I had a problem with a desktop on my laptop, 
it disappeared after an update. I created a new username and password, 
which I can use to log in, but when I go to look in Synaptic, it calls 
for just the old log in details, and I can dont know why, would anybody 
have any ideas?

John