Depends on the model. On some, you flip open the heads and push and turn the center locking mechanism until the heads release. On my razor you simply pull up on the entire head assembly.
It is possible to replace the head, as a matter of fact, a doctor in the 20th Century did it to 9 or 10 Reeses (I'm not sure if that's spelled right) Monkeys. However, while it is possible, the...
I replace the heads with first starting by draining the coolant then removing the exhaust as neccasary then the intake manifold and distributor then the valve rocker arms and pushrods then unbolting...