How to load C # object

We have retained the serialized value of some objects. Now we want to make significant changes to some objects.

So what I want to do is load the older version of the object using the old assembly, and then deserialize and serialize again with the newer version of the object. I can convert a method that can convert an old object to a new one.

I converted the object on the fly on the deserializer, but in this case it is almost a new object with the same name.