Upgrade Bw3.5 to BI7.0

Hi

We are about to upgrade bw3.5 to BI7.0,

can you please assit me on the this

1. What important things a should I know and do before start

2. what important things during upgration and after completion

how we should go about this being a BI consultant

any upgration doucment with steps ,

all useful ans will be highly appreciated.

thanks

Milli