Document Styles > showing "checked box" as grayout for contract,blanket

Hi,

how to uncheck the document style, we don't want to use the document.

ex: complex po document

check box : standard PO > complex PO ———— want to use

check box: contract pa> cpa xx ——- not to use

check box: blanket pa> bpa xx —- not to use

Navigation : Purchasing Responsibility > Setup > Purchasing > Document Styles

Thanks as dear experts.