In Link when it is talking about "Handle Conflicting Installation Methods" how I can know what X.Y would be? I am using ubuntu 16.04
If you have cuda installed you can get the version from the directory name or from the name on the uninstall.pl
ls /usr/local/cuda* ls /usr/local/cuda*/bin/uninstall*
Will yield "/usr/local/cuda-X.Y/bin/uninstall_cuda_X.Y.pl" where the X.Y you are asking about is in the cuda directory and on the uninstall script (uninstall_cuda.X.Y.pl).
Or you can also
Regardless of the version , you need to first uninstall it as directed before you install a new version.