virtualbox.org

I am trying to upgrade my Virtual on Yosemite, but the installation fails. Any help ! I don't know where to check logs of installation. Thanks in advance.

Take a look at this: viewtopic.php?f=8&t=7766#p301701

Thank you Socratis for your help.
I have got this error:

installd[734]: ./postflight: (kernel) Can't unload kext org.virtualbox.kext.VBoxUSB; classes have instances:
installd[734]: ./postflight: (kernel) Kext org.virtualbox.kext.VBoxUSB class org_virtualbox_VBoxUSB has 1 instance.
installd[734]: ./postflight: (kernel) Kext org.virtualbox.kext.VBoxUSB class org_virtualbox_VBoxUSBClient has 1 instance.
installd[734]: ./postflight: Failed to unload org.virtualbox.kext.VBoxUSB - (libkern/kext) kext is in use or retained (cannot unload).
installd[734]: ./postflight: (kernel) Can't remove kext org.virtualbox.kext.VBoxDrv; services failed to terminate - 0xdc008018.
installd[734]: ./postflight: Failed to unload org.virtualbox.kext.VBoxDrv - (libkern/kext) kext is in use or retained (cannot unload).
installd[734]: ./postflight: /Library/Application Support/VirtualBox/VBoxDrv.kext failed to load - (libkern/kext) different version/uuid already loaded; check the system/kernel logs for errors or try kextutil(8).

Here is the attached log file I have got. Thanks again.

Something is using the .kexts that are mentioned (a stuck process?). Steps to resolve:
1) Reboot your computer.
2) Run the VirtualBox_Uninstall.tool.
3) Install VirtualBox.