If VirtualBox is only showing 32 bits versions ensure to follow these steps:
Ensure your Host OS is 64-bits
Enable virtualization in the BIOS (Ensure Intel Virtualization Technology and VT-d are both enabled in the BIOS).
The Hyper-V platform is disabled in your Windows Feature list,
i.e (check that Hyper-V is not running or even installed on my Windows. Same for VMware).