Sorry bud, you'll have to make a new zoo, try one or two sizes bigger. I have some tips for making it so you can get the most out of your space.
If it is animal buildings (insect house, reptile house, theater) stick to the 3 or 4 that get the most guests.
If it is just bulky animal cages, think of what size they are. Don't make them larger than you have to. Also, don't EVER resize the cage because it can't hold all the animals unless there are only like 2. Just sell the animals 1 by 1 (and wait a minute or two in between) untill they are happy again. If you have only 2 animals and it isn't big enough, no choice but to resize...
If it is simply all the food those fat guests demand, I have 1 answer: CAFES!!! All you have to do is by a cafe and make it only 3 or 4 dollars to buy. Add a large bathroom next to it and you are done. This is actually cheaper because you take away multipule machines, picnic tables, trashcans, and sidewalk.
I hope that covers it, and if there is a different case that you ran out of space for, just post it.