How do I change Community user ids? I have 2 accounts but when I sign in to Community it always signs in with the wrong one. How can I change it to the correct one?

Click on the People icon at the top right of the screen.  Click on My Settings.  Your Username should be shown.  Click on the button labeled Change Username

I did that but it says that the other one is in use and wants to create a new one. I don't want another user id.

Try these steps before you follow DoninGA's steps.

• Clearing your Cache and Cookies
• Using a different browser
• Opening an Incognito Window