If they are just "regular" 4-day tickets bought with a FL resident discount, you should be able to change the date. Sometimes that can be done online through
MDE but not always so you may need to call to change the dates, and pay any additional if your new dates cost more.
If they were special tickets like the Discover Disney 4-day or something, those usually have a set window and must be used within that time frame. If completely unused, the credit can be applied to new tickets (which may not be the same type of discounted ticket); but if only partially used within the designated timeframe it will hold no value past the expiration.
So basically -- a fully-unused ticket will have value as a credit towards new tickets. Those new tickets may or may not cost more, especially if you had a discounted ticket but that discount is no longer offered (or not offered for the new dates). You will probably need to call to make any change.