I've purchased bonus tickets online and on the phone with El Al. But I have an upcoming flight BKK-TLV which has been reverted to the dreaded 767. I'd like to have the option to jump on a guaranteed upgrade just in case I don't change and fly a different day. I recall once asking to use my points at the airport and being asked if I had a voucher. So how do these vouchers work? What is the best way to redeem an upgrade at the airport or as close to departure as possible assuming the Last Minute Upgrade may not clear?