I have been using vegas platinum 9 and have now upgraded to 11. I still have 9 on my PC and am continuing a project I started in 9 now using 11. How can I safely delete 9 without losing any projects or data or settings etc.
You don't need to uninstall 9, at least not right away. Actually, it's probably best to keep 9 on your PC until you're satisfied 11 is working properly for you.
They occupy different folders so as Steve stated, uninstalling one won't affect the other.
And it's helpful (essential?) to make backup copies of your version 9 .vf files *before* opening them in version 11. The files are not backward compatible. Any file saved from Version 11 will never open in version 9 again. So, if you decide that version 11 won't get that project finished for some reason and you have to go back to 9, you'll have to use files that have never been touched by version 11.