Bitcoin version conundrum Given that the Bitcoin node software not centrally controlled (auto updated) and many different versions and implementations exist around the world, how would a core change be possible if it is not forced to all nodes? Example one would want to make the block size larger or change the hashing algorithm to be resistant to newer technologies like quantum computing attacks, not everything can be made backward compatible. How can one ensure that the newer improved core makes it to the many nodes that exist.
how would a core change be possible if it is not forced to all nodes?


Simple, it can't be. You can't force a change, users must willingly adopt it.

The bitcoin network is very conservative in regards to changing network rules, especially the rules that keep the nodes in consensus. This is by design: users that engage with the network have a high degree of certainty that no single actor (or group of actors) can force a change on the network. You could say that the rules of bitcoin are enforced by the code, not by the whims of some future politician. As it is often said, the inherent difficulty to change bitcoin's rules is a feature, not a bug.

There are specific details depending on the rule change in question, but in general: making a change to the bitcoin network requires an overwhelming majority consent. To avoid messy fork situations, changes need to be planned carefully and accepted pretty much globally.