The full instructions are available with the firmware downloads.
Q1: There are a couple of ways to do it. There is a small Java Applet you can download with the firmware. Dell Storage Update Manger (DSUM). You download the firmware kit and DSUM will transfer it to the members and help you with process. It will also check to see if any drives need to have their firmware updated as well. That's two processes though.
You can also manually transfer the firmware kit to each member and upgrade them one at a time at the CLI.
Q2: Time varies a bit. The actual outage time is very small. After the firmware is updated you have to restart that member. It will actually restart the passive first to get to the newer firmware. Then it will failover to it. That takes 15-45 seconds depending on load. If the load were extreme could take a little longer. So best to do this in a quieter I/O time to minimize failover time.
You can upload the kits at any time so that will cut some time out the total process.
The upgrade time itself is probably 10 mins. There is no I/O impact at that time.
So probably allow a couple hours but outage time itself a fraction of that.
If you open a support case they can help you with this process.