If the installer gives you the option to "Repair" or "Uninstall," choose Uninstall . Restart your computer, then run the installer again to perform a fresh "Install."

Not if you want it to run on fresh Windows installations. In Project Settings → Packaging, you can disable "Include Prerequisites," but your users will then have to install Visual C++ and DirectX manually – an awful user experience.

This tool bundles several third-party libraries that Unreal Engine requires to function correctly on Windows. While the Epic Games Launcher usually handles these installations automatically, you may need to run the UE4PrereqSetup_x64.exe manually if you are building the engine from source or setting up a secondary machine like a Swarm Agent.

Includes versions for 2010, 2012, and 2013 (VC100, VC110, VC120) which provide the C++ libraries needed by the engine's executable.

# Check VC++ Redist (x64) exists Get-ItemProperty HKLM:\Software\Microsoft\VisualStudio\14.0\VC\Runtimes\x64 | Select Version

Or look for these files in C:\Windows\System32\ :

This guide explains what the UE4 Prerequisites (x64) setup is, why it fails, and how to download and install it correctly. What is UE4 Prerequisites (x64)?