Imac pc unable to change the @ on a uk keyboard

Please select a different keyboard layout
Click the Apple icon from your menu bar, select System Preferences, and then follow these steps.
1) Click Keyboard.
2) Make sure you're on the Input Sources tab.
3) Click the plus sign button on the bottom left.
In the pop-up window, you'll see a list of languages on the left and options for them on the right. You'll also see a preview of the keyboard layout.Select the language you want and then pick the option on the right. For example, French > ABC - AZERTY or English > Dvorak.
5) Click Add.