Rico:
You may use miles to upgrade at any time where there is an "A" seat available in inventory. Be sure to allow at least 2 weeks' notice - otherwise they'll have to FedEx you the certificates for $35(?)

Domestically, it's 5,000 miles each way on a "Y" fare. Double that for discounted fares.

You can check out the chart here:
http://www.onepass.com/asp/charts.asp?airlinecode=CO

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"I will not be pushed, filed, stamped, indexed, briefed, debriefed or numbered. My life is my own."