Yes, you may postpone or cancel a flight. Depending on the airline 𝟏-𝟖𝟑𝟑-𝟒𝟔𝟎-𝟏𝟖𝟑𝟖 and fare class of your ticket, you may be charged a change or cancellation fee. If you purchase an unrestricted fare, you can alter your flight without paying a fee (depending on seat availability).