Don't know an easy way since old styles will overwrite new styles of the same name. And you may not want that.
This is why it is always recommended to install new version "over" the old versions. This why the new is added into the old.

Otherwise, you can look for a utility which will do a comparison of both new and old directories and ID the styles are not in the new directory. Then you can copy and past them from the old to the new.

good luck