Newer vehicles seem to have an unlimited key to allow updates. Yours may require an FSC code for the vehicle to accept new maps.
The procedure is pretty simple. DOwnload the maps (several sources, some free, some charge), copy in the right format to your USB drive, turn the car on, insert the USB into the port in the center console, and wait a bit. If the files are properly arranged and the USB stick is properly formatted so the car can recognize it, you'll get a message on the screen. If you don't need a new FSC code, it will ask you if you want to install the maps, say yes, and wait. You can drive the car if you want. When it's done, it will ask you if it's okay to swap the old maps out.
If you need an FSC code, it will tell you to enter one when it recognizes the USB stick, you manually enter that, and then the process is the same.
There are ways to generate an FSC code if you're computer savy and have the right tools. It's easier for most to buy one. They come in either annual or lifetime codes, and the price isn't all that much different. Do a search, and you can find sources. Prices vary from around $15-50 or so.
I expect the 2019-2 version will be out soon, if it isn't already. They tend to change them 2x per year. The update process takes 30-45 minutes or so, somewhat dependent on the speed of your USB drive.
2011 535i x-drive GT, 2014 i3 BEV