It really depends on what kind of fern. If tropical, house plant type ferns then you will need to bring them in the first night that frost is predicted. Any house plant/container soil can be used for repotting.

If they are actually hardy, outdoor ferns you have a bit of a problem. Those ferns need to have a dormant period during the winter in a cool, dark place. Basement root cellers and unheated garages are good places to put container grown hardy ferns for the winter but you won't have those in an apartment. You could try overwintering on the balcony with a thick layer of straw insulation and keep your fingers crossed.

Here is a link that might be useful: Overwintering containers