For Premier Exec you can change as Rudi says. Same day changes are waived for PE & 1K. For 1K only, different day changes (lv on Tues instead of Mon) are waived if the same fare is available. The rules say they can charge you for a different day change if your fare is not available but as a 1K you may still get it waived. I think this applies to routing changes (1K only)as well.

I just did this on Tuesday. I flew IAD-BOS in the am and was ticketed to return the next day. I called my corporate travel agent and she was able to change it for me so I could fly back that evening with no penalty. I didn't ask if the same fare was available