Replacing a computer program with a replacement version concurrently with its execution by a first instance of an operating system in a computer system, wherein a persistent memory area in the computer system is used to store selected data from the first instance. A snapshot image of a second instance of the operating system, wherein in the second instance the replacement version was executed instead of the computer program, is provided to the computer system. The execution of the first instance is suspended and the first instance is replaced with data from the snapshot image while preserving the persistent memory area. The execution of the first instance is resumed and data from the persistent memory area is restored in the first instance.