Currently, to delete a custom field, you need to customise the layout of the record type, go to add a field, expand to custom field, choose 'add custom field', select the type of custom field you want to remove, and then when provided with a list of current custom fields and open custom field spaces, you need to erase the name of the custom field you want to "delete".
This then also does not delete any data stored in this field, so to update that you would need to bulk update the field first to be empty, and then delete the field.
