Changing Flight
 

I'm attempting to change an August 5th flight to Denver, to August 4th.
I made a suitable choice for the 4th but I'm unclear how to 'lock' my choice in.
Of the selection choices I can 'select this flight'
Then at the top press the update button to save the changes.
However when I go back to Trip details it still shows the 5th.
Same on the app.

You are stopping a few steps too soon.

"Update" refers to the search, not to selection the new flight. If the flight you want appears, ignore Update
Once you get the potential new flights options, click on the desired flight just like what occurred at purchase
Then you will go to a "review" page, it it is the right flight hit "continue
Then you will have a chance to select seats
Then continue to Checkout
Then process the new fare difference
then confirm

I'll try...thanks...