How can I update a file in Google Docs?

I use Google Documents between my school and my house. Say I am writing a paper and I don't complete it, so I upload it to Google Docs to work on at home. Then, I download the file to my home computer and work on the paper a bit more. So then...how do update the old file in Google Documents? If at all?





Thanks.|||Click on the box next to the document in google documents to get a tick in it.





Then click on the dustbin (trash can) button above to delete it (Moves it to trash).





Finally, upload your document again