You should be able to uninstall if you have to. I don't think there is much left after in-place upgrade. SQL server engine, SSAS, SSRS, etc should all be upgraded, new SSIS 13.0 should be installed, maybe SSIS 12.0 and SSMS 2014 are uninstallable if you don't want them.
If it's side by side upgrade(named instance for SQL 2016), yes, you can uninstall more, including instance and shared components of SQL 2014.
please test it for your own environment, clustered instance could be very different than standalone instance.