Can I update to Cubase 10 with 9.5 still working?

Hi. I bought a crossgrade to Cubase 10 from 9.5. If I install it will I have two programs installed 9.5 and 10 or 9.5 will be changed to 10?

You will have both, they are completely separate installations. either can be run. I have versions going back to 7 installed on one of my machines without issue.