Removing custom fields
To remove the custom field, open up the sequence's settings and select the "Fields" tab. From there, click on the trash bin icon for the custom field you'd like to remove. Be sure to click "Save Changes" to save this change.
Re-adding removed custom fields
You can re-add the removed custom field by entering the name of it in the "Fields" tab. It'll restore the contact's data for that custom field so you won't need to re-enter this information in again.
Note: If the removed custom field appears in an email step within the sequence, this won't automatically be removed. You'll need to edit the email step if you don't want to include the removed custom field.