Access the link posted below and enter the following term: "Extensa 5635Z" (without quotes). There is a ZG version, but you need the one without the G. Click it and the frame with the downloads will load. Select the operating system (Windows 7, Vista, and XP in 32 and 64bit mode are supported), then download the necessary files to your computer.
Make sure to click the Application tab as well to download the available companion apps like Acer Updater, Acer Launcher.