You can't download Windows 11 to your computer.
If you want to install Windows 11 on your computer, and you are certain that your computer's hardware qualifies it for Windows 11, download the Media Creation Tool from Microsoft's website and use it to create a Windows 11 installer on a USB flash drive. Then, boot your computer from the flash drive, and installation will commence automatically.
Here are Microsoft's detailed instructions: Create Windows 11 Installation Media