Having roots in Search-Based Software Engineering (SBSE), the relatively young area of Genetic Improvement of Software (GI) aims to improve the properties of exisitng software. It can operate directly on source code, e.g., Java or C, and it typically starts with real-world software. This makes GI attractive for industrial applications, e.g. in contrast to Genetic Programming that aims to evolve applications from scratch. In this tutorial, we demonstrate how we can optimise with GI the physical properties of code such as power consumption, size of code, bandwidth, and other non-functional properties, including execution time.