Which installation changes from the old information system to the new one incrementally, starting with one or a few functional components and then gradually extends the installation to cover the whole new system?

Phased installation

Explanation:

The name of this strategy is phased installation. Phased installation (or phased implementation) occurs when an existing system is replaced by a new one. However, unlike most implementations, this takes place in stages. This has several advantages. First, it allows you to test the system. If there is a problem with it, it is easier to revert back to the old strategy. Moreover, if employees need to adopt this new system, it allows them to get used to it slowly while still being able to access the previous one.