I am using sp 2010. How can I remove a userprofile from the User Profile Service Application in Powershel?
You need to get a reference to the UserProfileManager object, get the user profile object, and then call RemoveUserProfile() on it. Here is an example script:
Note that this particular script deletes ALL user profiles; you'll need to modify it to locate a specific user profile (using a login name, for example) before deleting just that one profile.