Steps to install VirtualBox 4.3.10 on Fedora 20. You need to first open a terminal and become root user:

$ su -
Password:
#

Install dkms package:

# yum install dkms

If Virtual Machine Manager is running, stop the same, and uninstall it.

# yum remove virt-manager

Remove the KVM modules if already loaded:

# rmmod kvm_intel

Download and install rpmfusion-free repo from rpmfusion.org:

# yum install rpmfusion-free-release-20.noarch.rpm

Install VirtualBox:

# yum install VirtualBox

Install the required VirtualBox kernel module for your running kernel. For example, on Fedora 20 with kernel 3.11.10-301, you can run:

# yum install kmod-VirtualBox-3.11.10-301.fc20.x86_64

Load the vboxdrv driver:

# modprobe vboxdrv

You can now start VirtualBox and use it. To convert Virt-manager images to VirtualBox, you can use:

$ VBoxManage convertdd ubuntu1204-lts.img ubuntu1204-lts.vdi