The present invention relates to a Software replacement method, for replacing a first software package that comprises a command handling interface which is present at a computer system, by a second software package over a connection between an operator terminal and this command handling interface. At first the second software package is installed besides the first software package at the computer system. Subsequently, the second software package is activated. Then a contacting part of the second software package, after activation of this second software package, contacts the command handling interface. The command handling interface at contacting of the command handling Interface by the contacting part of the second software package, switches from the first software package towards the second software package and keeps open the connection between the operator terminal and the command handling interface.