Some internet searches will turn up many hits since there are a few ways of running an msi installer as administrator on Win8. I would do it using an elevated command prompt like this:
-
Swipe in from the right edge of the screen, and then tap Search. (If you’re using a mouse, point to the upper-right corner of the screen, move the mouse pointer down, and then click Search. Or just press the start button in your task bar.)
-
Enter cmd in the search box, and then right-click or press and hold Command Prompt*.
-
Select Run as administrator from the menu. Click ‘yes’ when prompted by UAC. Once the command prompt window opens make sure it says Administrator: Command Prompt in the title bar.
-
Run the installer using the following commandline(NOTE: replace C:\EpicGamesLauncherInstaller.msi with the path to your installer. Don’t forget to include the .msi file extension.)
msiexec /i C:\EpicGamesLauncherInstaller.msi