replacing 13900k with 14900k

Hello gang! Can i just loosen the water cooling unit from the present cpu and just drop in the new one? Can I do it in place under my desk? the tower weighs a TON!!

And do I just go wth the heatsink compound that comes with the cpu or the fancy expensive paste that I bought three years ago and my regular builder refused to use? he beleives that stock paste is all you need. If do use the fancy paste can I just put it on top of the existing stock paste or do I have to clean it off first?

Any help appreciated. I will rma the 13900k, but cannot have down time.