my safari wont close, therefore i cannot update my mac

Press these three keys together: Option, Command, and Esc (Escape). This is similar to pressing Control-Alt-Delete on a PC. Or choose Force Quit from the Apple () menu in the upper-left corner of your screen. 

How to force an app to quit on your Mac - Apple Support

If you cannot Force Quit Safari:

Check for adware.

     Run the latest release of Malwarebytes for Mac to remove malware/adware, if installed on your Mac.

     For instructions:  Install Malwarebytes for Mac v4          Uninstall Malwarebytes for Mac

     Click the “Scan Now” button. Once done, quit Malwarebytes for Mac.

     Restart the computer and relaunch Safari holding the shift key down.

If the above doesn't work, shut the computer down using the power button and then restart.