I have the 4020 on my A and it's as far as I'll take it, but you need 3810 first to reconfigure the HDD.
You'll need to reload maps from DVD as they'll have been wiped, however cos of the repartitioning from 3810, you'll not lose them in the future.
Might be worth using a laser cleaner on your stereo, that link I put up definitely worked on the cars I did. You'll get there!
Just checking, are you using a CD and not a DVD for firmware? I did.