Offline maps update available for Windows Phone users
Checking for these updates is as simple as going to Settings, swiping to Applications and clicking on the option for maps. Toward the bottom of the screen, you should find an box to click that will check for updates. Tap on that box, and your phone will search for updates covering any of the regions you have installed for your offline maps.
If you're lucky enough to own a Windows Phone model with a microSD slot, you can store some of the offline mapping data on your card to save the native memory on your phone. While you are updating your offline maps, you will be unable to access them, so obviously you need to pick a time to update when you do not expect to need the maps.