Most airlines do allow date changes to your ticket, but it is important to note a few things:
1. If there is an increase in your base fare and/or taxes, these will need to be charged to you at the time of changing, in addition to the airline date change penalty and a Travelstart handling fee
2. Airlines generally require you to change your ticket at least 24 hours prior to your original departure date
3. Each airline has its own rules pertaining to different fare classes