Once you started you're campaign, it can be the case that you added someone you didn't wanted to add.
You are able to delete contacts from an active campaign. I'll explain you what to do.
Go to Expandi
On the dashboard you click on campaigns.
Select the running campaign you want to remove you're contact(s) from.
Click on the action tab and select the people you wish to delete.
Select the people and click on delete selected contacts.
See the screens below.
7. The selected contact will be removed from the campaign.