Before you start make sure you download the June Update Pack for the SP3 from the link in the first post, I would save it in your downloads folder personally and unzip it there...
Step One - Open up Device Manager (either through the Admin Control Panel or Navigate to it from Computer Management MMC by right clicking on the "This PC" Icon in the Tree View of an explorer Window and selecting Manage
Step Two - In Device Manager navigate to the Network Adapters and expand
Step Three - Right Click on the Marvell Avastar Wireless Network Controller and Select Uninstall - when the dialog box comes up check the box that says Delete The Drivers Software from this Device
Step Four - Reboot
Step Five - Plug and Play will install the Original Drivers (Unless you've ran disk clean-up and removed a bunch of stuff)
Step Six - Adding this as it was pointed out to me, run Windows Update and it will offer the June Updated Drivers (I hid this Update as I didn't want it to install it)
Step Seven - Return to Device Manager and navigate to the Marvell Avastar Adapter and right click and select update drivers, tell the Update Wizard to browse your computer and navigate to C:\Users\<yourusernamehere>\Downloads\Surface Pro 3 - June 2014\Marvell\wlan and allow it to update...
And you're done....don't update anything else, don't over think, keep it simple.
If you are not comfortable with this type of stuff - DON'T DO IT!!! Microsoft is working on an updated driver that should be available shortly