Uninstalling a program using the system's built-in uninstall feature is the best option to remove unwanted software because it is designed to safely remove all components of the software from the system, without leaving behind residual files that could take up resources or cause conflicts. Rebooting the computer or deleting the program's desktop shortcut would not remove the actual software from the system. Defragmenting the hard drive could improve performance but would not remove any software.