Under My Settings there are a couple if Contacts Settings that you can manage.
If you want to be able to upload a file of unsubscribes you can check in the box to enable advanced permissions and click to Save.
You also have the ability to manage all of your custom fields here. This is best if you want to Delete a Custom Field for all contacts or adding a new custom field to your account. After clicking Manage you will be brought to a page showing all Custom Fields. To delete one click the X. Please note that if you delete a custom field it deletes all of those fields for your contacts and the information in those fields will not be available in your account. If you might need this information in the future I would recommend exporting your contacts and saving the file with the custom field information before deleting.