We need to review all elements modified in the templates between 2.5 and 2.6 and write and test an upgrade procedure for existing clients that are in 2.5.

This usually includes removing elements, adding elements, modifying them, coordinating reboots etc... because some changes break compatibility between releases usually. For example in this release we have renamed some ImageStream tags. This means that a new tag has to be created manually, the latest tag of the imagestream has to be updated pointing to the new tag, the pods that use them have to be rebooted, you have to provide a way to check that everything is ok after the changes, etc...