Thanks for your interest in Aspose.Slides.
I have observed your requirements and like to share that HeaderFooter class exposed by Presentation class may help you to control the header and footers display in presentation slides. You can try using the following sample code to hide the Slide number from footer of presentation.
pres.HeaderFooterManager.IsSlideNumberVisible = false;
Please share, if I may help you further in this regard.
I have observed your further comments and request you to please provide the source presentation and desired output presentation without slide numbers. I will investigate the requirements and will then be able to share further feedback with you in this regard.