If using XAMPP local hosting, copy to xampp/htdocs/ folder. Or else host the folder on your server like any other file (assuming you have apache support). 
Then visit http://yourIPAddress:port/wupinstaller on your WiiU browser.
It will kick you out of browser, choose browser again and visit that URL again. It will kick you out again, this time press Home button.
You should get an error code and the WUP files you have in your SD:/install on the Wii should be installed now. (if it's a big install like SSBU update, leave the error screen on for a few hours or so before forcing rebooting just to be safe, it's installing in background)