Changing Administrator Password Without affecting your Exchange Server 2013

Hi

I am running Exchange server 2013 on a Virtual Machine as well as My Active Directory Server on another Virtual Machine hosted on an physical Machine running Window Server 2012, and I want to Change the Administrator Password on all there Machine but I'm scared it might affected my Exchange server mail flow, its because I did once change the password and it affected my Exchange Server.

Can any one tell me how I should go about changing the Administrator password on all Three Servers without affecting my mail flow on exchange server 2013..??

Thank you