Will upgrading to a new version of Bitcoin Core leave my wallet intact? If I download Bitcoin Core 0.14.1 to my Windows 8 drive will it simply overwrite my existing Bitcoin Core version v0.11.2 (64-bit), leaving all my BTC in my wallet intact?
In the case that you mean "install" instead of download: Yes, it should not interfere with the wallet.dat at all, and the new version of Bitcoin Core will continue to work with it.


Regardless of your updating the software, you should have at least one backup of your wallet.dat. If you don't, create some now. Preferably before the software update. Be sure that Bitcoin Core is not running when you copy the wallet.dat.
Be sure to close Bitcoin Core before installing the new version.