You can't. They are platform specific.
Since they are current versions you might contact customer service. Believe you can switch platforms, not sure if there is fee involved.
If you sign up for Cloud they can be used on either platform.
The Lightroom serial number is cross-platform. It will work on Windows and/or Mac.
Download the LR4.4 Mac installer
Enter your LR4 upgrade serial number. You'll alo be prompted to enter the serial number from an earlier qualifying version. Enter an LR3, or earlier version, serial and LR4 will be licensed on your Mac. You're entitled to 2 installs per license so you can leave it on your PC too if you wish.
In terms of moving photos and catalog to your Mac, see
The Photoshop CS6 serial number is platform specific. Your Windows serial number will not work on your Mac.
Either follow this process to permanently swap platforms
Or join the Cloud. Cloud apps can be used on Mac and/or Windows.