How does one use an e-Voucher for an upgrade and check for Upgrade availability before booking a flight, do you have to book on LH direct to use this or can you book on a third party site like Expedia?

I have been looking at booking EDI-FRA-HKG for October in C and was wondering if Senator 2 e-Vouchers would be enough to upgrade to F but can't find out about upgrade availability?
Tried navigating the LH Web Site but this is a bit of a minefield (and I thought klm.com was bad).

Also if I search for an award to Hong Kong the site does not recognise HKG or Hong Kong as a destination!

pmcg