I need to fly in and out of SJO and was able to use DL miles to get a CO ticket since they are Skyteam partners. My question is that the day I need to fly only premium awards are available. If I get the ticket issued and if there are seats available on the day of travel, can I get on the flights I am really wanting to take. This is also an e-ticket so I should be able to change it as long as there are seats available. Is that correct or does CO has different policy - any fees associated with this change?

Help!