First, you must realize that you will, or should, receive a copy and any paperwork going back and forth in regard to the lawsuit.
It sounds as though the plaintiff filed a motion requesting permission from the court to amend their original complaint against you. Amend means to change. The court has granted the request, and you received a copy of that response to the motion.
A request to amend a complaint is usually freely granted but can be denied under certain circumstances. Here, it was granted. What the plaintiff wants to change is unknowable from the question itself. An informed guess would require knowledge of the original complaint, of how far along in the process the suit is, and of the procedural history thus far.
If you do not have a lawyer handling this with you I suggest you consult with a few immediately and get someone to assist you.
It may well mean that the Plaintiff (the mortgage company) made a mistake which they are now trying to correct. Unless someone who really understands this stuff looks at it, you will not be able to tell what the error is (if any), or whether it can be useful to you. Further, the fact that a motion to amend was made may mean that it was not made possibly, or not noticed properly.
If you care how this goes, you really need to consult an experienced foreclosure defense attorney.
When a complaint is changed in this manner, you should have someone look at it who is a Florida Foreclosure Defense Lawyer to make sure the changes are permissible. Often we see changes in complaints were they substitute one Plaintiff for another or where the terms of the complaint are changed to reconcile with what the evidence will show.
You should have this reviewed soon to file any objections or motions that are proper based on the changes.