Upgrade to 8.1.7 from 8.0.5.2.1

Hi guys,

We are running two databases on 8.0.5.2.1...my scenario is we are doing replication across these databases..
Database A having schema EMP
Database B having same schema EMP

'A' is the master database and I have created read-only and updateable snapshots in 'B' on EMP schema..
They get fast refreshed every night.

Now I want to upgrade both of these databases to 8.1.7..not necessarily at the same time..

What are my options and how can I do that??

I heard from some body that I need to rebuild my snapshots after upgrading which means a week of loss of service as there are so big tables in Database A that it takes lot of time to rebuild snapshots on them...Both databases are miles apart and data flows thru WAN.

Are there any faster ways to create snapshots like export and import and somehow tell oracle that start refreshing from there..??

Please help..

Thanks