Miles & More (Lufthansa, Austrian, Swiss, and other partners) - Upgrade on OS?

Flying on OS in Nov in Q on TATL and to BKK on 763 and 772 respectively. We are currently in rows 21 and 17, should we try to upgrade to the exit row or will it not matter much (we're not tall or big)?

We are checking in w UA in BOS then onto IAD for our first OS flight. Would we have to try to get the upgrade in IAD? Any ideas on cost for upgrade to exit row or even biz?

Not sure if anyone would know but if we do upgrade - what happens to our fare class?

Exit row purchase can be done during online checkin. More details here:

http://www.austrian.com/Info/AtTheAirport/RedServices.aspx?sc_lang=en&cc=FI

Its called red|space and costs 70€ per person... the booking class remains unchanged. The upgrade to business will change your booking class to P.