You can manually edit/manage contact details and preferences. Here is a quick guide how to.
1. Go to your Contacts screen
2. Click on the edit icon
3. The Edit Contact window will open
You can edit their basic details here, add/delete tags and their marketing preferences (for example if they call you to tell you they don't want to receive anymore emails from you, you can check the box that says "This user does not want to receive marketing emails".
Once you've made your updates click Save and they will be applied.