How to upgrade from 1.7.5 to 2.0.0.8 without problems

[-marco-]

Hi

I have backed up of my old fengoffice 1.7.5
now I need to upgrade manually to version 2 but I need some tips for that.

Now my db have  _fo and _og. I have to delete one of these?

sorry for my english and thank you for you help (I hope)