So far as I know, it is not possible for you to “delete” sacramental records. The records do not belong to the individual but to the diocese, and the diocese may have need for those records in the future. For example, if you ever choose to re-convert, the records will be necessary to establish which sacraments you have received to date. Or, if there is ever an annulment sought through the Church, whether it be by you or by a spouse, those records will be necessary for adjudication of the annulment.
If you feel strongly about making a formal statement about your “de-conversion” (for lack of a better word), you could write to the bishop of the diocese in which you live to notify him of your defection from the Church. You might even ask that note of your defection be made in the sacramental records.
