Remove signature from CMS message

To remove an existing signature from a CMS

Load your CMS structure into a TElSignedCMSMessage object as described here.
Locate the desired signature in the Signatures[] list.
Pass its index to the TElSignedCMSMessage.RemoveSignature() method: cms.RemoveSignature(0);
Save your updated CMS with the Save() method. Note: while being a bit unusual, a CMS with no signatures perfectly complies with the standard.