If you don't have proper storage then freezing would be the best option. Detailed instructions on how to cook and freeze below.

Some cooking will be required first just to get it out of the shell but how much depends on how you do it. Some bake, some boil, I prefer to microwave mine until soft enough to cut and remove the rind. You can then freeze it mashed or in chunks.

Dave

Here is a link that might be useful: Freezing winter squash