Once the files are downloaded you need to copy the "root.zip" file to your Galaxy Ace 3 sdcard root folder.
Now install Samsung USB drivers on your PC
Once you have installed the drivers enable "USB debugging mode" on your Galaxy Ace 3 and switch it off.
Now enter it in "Download Mode".
To enter Samsung Galaxy Ace 3 in "Download Mode" press and hold "Home"+"Volume Down" and press "Power" buttons until you see a warning screen like the one given below,