I accidentally changed my iCloud password and username online, and now cannot sign out of iCloud from system preferences? Is there any way to manually delete sign in files so it can reset?
Won't let me sign out of iCloud from System Preferences
Many people had this same issue. I solved it by deleting all files from the following folder:
/Users/<YOUR HOME FOLDER>/Library/Application Support/iCloud/Accounts
Then reboot.
I was then able to get into the iCloud preference pane, where it asked me for my new password. After giving it, all was working again.
hmmm but what if I need to change the username as well? When I press sign out, it gives me the error saying turn off all iCloud services and try again
Assuming you've deleted the iCloud account files and can now use the iCloud pref pane normally, then you should be able to control many of the iCloud services from there.
You may also need to manually sign out of Messages and Facetime (options that are accessed through the main menu items for those apps)
However, I didn't need to sign out and back in again after iCloud got itself stuck because I changed the password. Everything started working properly again when it recreated the account file in the location mentioned above.
Also many people (10 or so) had similar issues and reported that the above fix solved it for them.
Hmmm I think it's because I changed my username as well, so essentially the stuck account is nonexistent.