how can you update Mac Pro retina 2012 to new OS?

Your 11 year old computer is not supported for running later versions of macOS, which are much more graphics-intensive, and require additional hardware-assists that are not built into your computer.

hobbyist hackers have produced ways of installing later versions, but important features (such as Wi-Fi) drop away rapidly. One posted a summary that Macs as old as yours were 'Unusable' because their graphics were so slow when running newer, unsupported MacOS.

Your Mac can still do everything its could do the day you took it out of the box, and a whole lot more that Apple has provided in the intervening years.

if it is inadequate, it is your NEEDS that have expanded, not an inherent shortcoming in your computer.

You can upgrade 2012 model MacBook Pro Retina display to MacOS 10.15 Catalina, the last-supported macOS for that model.

Mac Pro is a 40-pound silver tower computer that does not include a dedicated display.

If you decide to look around at new Macs, there is one more thing.

Technology has been moving rapidly, and the compute power of much lower-end Macs will far exceed most Users' needs today.

Be sure to look at the entry level MacBook Air and the high-end iPad as well. The MacBook Pro is trying to cover video editing at the same time, and may be more computer than you need.

Be sure to buy more RAM and drive space than you think you will EVER need, because its not expandable after purchase.