How to reset user name and password

I downloaded eM Client only yesterday but am having problems with settings.  I’ve lost track of what user name and password I entered originally but am getting an error message when I try to send or receive.  Can you advise?  May be simplest to reset settings…

Hello John,
if you forgot your password to your mail account, you need to contact your mail provider or check for reset options on your mail provider’s website.
There is no user name or password needed to use eM Client itself.
The only credentials you get from us and which we have access to is the credentials to our licensing server, but since you are still using the DEMO, none has been assigned to you.

If the problem is not with your password to your mail account, please share any error messages you might see and the content of Tools>Operations>Log so we can assist you with your connection problems.