change domain password

I login to a works, Windows messenger SIP.

When I first set it up it asked me for username i.e. and then asked
for my domain\password

I have had to change my domain password yesterday and now I cannot login to
messenger. If I say login as different user I can only use my same email i.e
.... it doesnt let me have the option of changing my domain password?

Which Im guessing is the reason it wont let me in? as it has my old domain
password stored in it???

Any ideas

Cheers