Change domain password

I login to a works, windows messenger sip.

yesterday i had to change my domain password and now i cant use messenger.

when i first setup messenger it asked for my username i.e. a.RemoveThis@b.org and then
my domain\password

even if i try to login as a different user i can only use a.RemoveThis@b.org and it
doesnt give me the option to change my domain password for the connection. Im
guessing that is why i cant login?

I can remove messenger and reinstall and then setup my connection with
correct credentials but there must be a better way???

Any ideas?

Cheers