I did make sure that I got the correct maps against the navcore for both the 883 Africa and 885 Eastern Europe and Western & Central Europe 2GB versions.
I was hoping to update to 890 for all three but there are no meta.txt files for the versions that run with my navcore, and I am a bit unsure about installing a different navcore.
Having said that I did read that you also need to install a new Boot Loader file and if it don't work then your TT is scrap, as you cannot undo it and go back!
because of the way the new maps are fixed then it is more difficult to get a proper meta for the latest maps, you only need a new bootloader if yours is very old and as your unit has a built in hard drive then you do not need to update so you can use a larger sd card, if you flash a newer bootloader you need to make sure that your unit is fully charged and connected to the mains charger, that way if you lose power at least you have a secondary power supply, you can actually go back to an older bootloader using a special boot flash but in your case i would just flash version 5.5242. After you flash your screen will go a blank white with a please wait warning then it reboots by itself so do not interrupt it once you have placed the bootloader onto the drive and disconnected from your pc.