Download Geth from https://geth.ethereum.org/downloads/ (Update, April 3rd: https://ethereum.github.io/go-ethereum/downloads/).
Note: There is an “Installer” version and an “Archive” version. You can go with the “Installer” (even though it was once deemed suspicious by my Antivirus software). But probably okay to download the 64-bit “Archive”, unzip it and move the geth.exe into Program Files\Geth\ instead of the older geth.exe file you had there. Less important: I believe the “Installer” does more stuff, namely to try to change the PATH variable (it didn’t succeed in my case), and to update the uninstall.exe file as well…
Run certutil -hashfile __path_to_file__ MD5 to compare to MD5 in website.
Download Ethereum-Wallet-installer-*.exe from https://github.com/ethereum/mist/releases/.
Run certutil -hashfile __path_to_file__ SHA256 to compare to SHA256 in website.
Run the installer. IMPORTANT: It may suggest to place the blockchain data in:
C:\Users\___your_user_name___\AppData\Roaming\Ethereum. Here you may change it to D:\Ethereum instead, if you prefer an external drive.
Optional (recommended): Create a shortcut with --syncmode "light". In fact, the “Target” in the shortcut can be something like: "C:\Program Files\Ethereum-Wallet\Ethereum Wallet.exe" --node-syncmode "light" --node-datadir="D:\Ethereum"
Note: No need to run both geth and wallet. Just run the wallet (using that shortcut you created!), it will invoke the proper geth.