If you are using certificates to upgrade at the airport, they are first come first serve, if seats are available. Once there is a waitlist its buy elite category, then time of check-in.

First check expedia or itn to find out if there are first class seats available. I suggest doing this the night before. You can also call the elite line and ask them to check. If there are none, then your space available certificates might not do you much, since the Higher elites will jump ahead of you on the wait list.

As for the plane's the 737's have up to 14 First class seats, depending on the model.
If I remember the 737-700 has a good ratio of first class to coach.

If their are first class seats then being first person in line at the airport will help big time.

As for the reply that said the certificates will be useless after 3/1, NOT TRUE.
I have right in front of me an ELTS that has an expiration date of 4/8/99.

Good luck on the upgrade.