You can find the file autoit-v3-setup.exe from the link above. To protect the system, please check the file with the antivirus program. Use your own solution or try a free one – Panda Free Antivirus.
Download the 11.7 MB and start the installation by clicking on the file and following the steps of the setup process.
You won't face problems with uninstalling the program. Click Start and then Control Panel. Choose AutoIt and press Uninstall.