You can also use the ArduinoISP sketch (File > Examples > ArduinoISP) to use one of your UNOs as an In-circuit System Programmer to burn a bootloader onto one of the new chips.
You can also use the ArduinoISP sketch (File > Examples > ArduinoISP) to use one of your UNOs as an In-circuit System Programmer to burn a bootloader onto one of the new chips.