There are several ways to remove people from campaigns:

From the Menu:

Go the person’s record and select File / Remove from Campaign.

Edit the Campaign:

Go to the Campaign Manager and edit the campaign. Click the Target List tab and remove the person from the list.

If you created the Target List using a query, you can rerun the query and select Remove People Only from the options. People not selected by the query will be removed.

Viewing Campaign Status:

Go to the person’s record and select View / Campaign Status. Then click Remove.