Data center operators today are tasked with helping achieve corporate sustainability goals, including net-zero emissions commitments. Aging physical infrastructure is a significant obstacle to this effort. In addition to posing downtime risks or added maintenance costs, this infrastructure can negatively impact efficiency and environmental sustainability. But operators may struggle to understand how modernizing their power and cooling systems will help them meet their sustainability goals. In this paper, we describe the challenges that aging infrastructure pose to your environmental sustainability goals and present three approaches to modernizing data center infrastructure systems. We then provide specific examples of how each approach leads to improved sustainability and discuss seven key factors that help assess which approach(es) to take given the breadth and complexity of systems in a typical data center.