My computer stopped updating the software , I am trying to install a new printer and it tells me to upgrade my operating system before installing my printer , But cant upgrade the OS?

There are two possible options open to you.

1. If this is a new printer it will likely operate using AirPrint which does not require any printer drivers. See if your Mac can use that method.
2. Otherwise, check on the printer's web site to see if there is available a driver that works with your Mac's operating system.

Good luck.

I should add that sometimes even if there is not a driver for your specific operating system, another driver might work.