Insert name of user you would like it to be removed from in the url (replace steamit2), then go the the url
https://v2.steemconnect.com/sign/undelegate-vesting-shares?delegatee=steamit2
Next you will get this screen, click continue,
Next it will show you the confirm login screen, insert login name and password, this will be the delegator user (this case plainoldme)
Click sign in.
And that's it, you have successfully removed delegation from a user.