I am a new Premier Executive, and have a question about the 500 mile upgrades.

I called yesterday about a trip for my myself and my wife (non-Premier) (CMH - SFO)the end of April. The ticket agent was helpful in setting everything up and also put we on the waitlist for Upgrades.

It sounds like on this trip I would need 5 500-miles for each way per person (20 500 miles). I don't presently have that many, and it could get expensive to pay for these to upgrade (although less than a First Class Ticket).

My question - what happens if I am on the waitlist and decline the First Class upgrade ? Do I lose my Economy Plus seat ?

Also, if I needed, say 5 500-miles, can I purchase those on the day of departure ?

Thanks for any information