twitter

Which application?

There are loads of Twitter apps all with different solutions which can probably be found in the instructions or settings.

No idea - I don't use that one but the answer to your question is certainly in the configuration settings like most Apps.

Contact developers website - support@iconfactory.com or of course, hang around here until someone who uses it arrives (I use Tweetdeck)

I use the paid version of Twitterific and if you go out to "Sources" and then press Edit, then select the account (which will have the "delete" badge next to it). This will bring up the login details for the account. If you delete the login name and the password and then back out to Sources and tap Done, you will be logged out.