To rename a file in Windows, the shortcut key used is F2. This keyboard shortcut is a quick way to rename selected files or folders without using the mouse. Here's how this works step-by-step:

1. Select the file or folder you want to rename in Windows Explorer.
2. Press the F2 key on your keyboard. This action activates the renaming mode, allowing you to type a new name directly.
3. Type in the desired new name for the file or folder.
4. Press Enter to confirm the new name.

This shortcut is widely used in various Windows versions, from older versions like Windows XP to the latest Windows 10 and Windows 11.

Let's evaluate the other options given:

• F3: Typically used to initiate a search function in many Windows programs, like Windows Explorer.
• F8: Commonly used to access the boot menu in Windows during startup, not for file operations.
• F6: Often used to cycle through screen or focus elements in some applications, but not for renaming files.

Therefore, the correct answer is F2.