Show / Hide ribbon button

Hi,

I have created  custom button on Ribbon.

I need show / hide that button based on security role  ( for example:  if user "system administrator" , then show button ).

I have read this: http://www.powerobjects.com/2016/05/17/solving-security-headaches-display-rules-based-on-security-roles/

but I do not understand where is the part where I check if user "system administrator" or something else.

Please help me...

Thanks in advance...

Kind regards

Martin