WinUSB Driver
Windows have WinUSB driver files in system folder from the begining. You don’t need to download from somewhere.
To install WinUSB driver for your device follow steps below.
First, You need to start Flash mode and find your device in Device Manager.
To start Flash mode push button on your device.
Right click on Widnows start button and select 'Device Manager' from popup menu. Or press Windows+R and type devmgmt.msc.
You can find your device under 'Other Devices'. It is labeled as 'ATmega32U2 DFU' or 'ATmega32U4 DFU' probably.
If you cannot it will be located under 'LibUSB-Win32 Devices' or under 'Atmel USB Devices'. This means that different driver is already installed. In this case you will have to select 'Uninstall device' from menu before installing WinUSB driver.
On Windows 7 you may have a problem. https://community.silabs.com/s/article/manually-install-winusb-driver-on-windows-7?language=en_US
You can install and run Zadig to install WinUSB driver instead of process above.