Depends how you're doing it.
Tomtom home is not ridiculously difficult to use, but the simplest way is to couple the TT to your PC and navigate to the folder with the maps in, and plonk the OV files there. Should then be recognised.
Unless, of course, they've revised the folder structure of the latest GO series. But that is how it works both with my '520 and her '930
What goes wrong?