On Android, how do resave a txt file on Dropbox programmatically?

The title more or less explains my question. I need to be able to pull a .txt file from Dropbox, edit the contents, and then save/republish the file back onto Dropbox.

I know how to retrieve the file from Dropbox and edit the contents, but publishing it back is where I am uncertain. The file is linked (via copied public url) to other users so it has to be saved as the same file from which it was opened. How do I push the edited contents back onto the original .txt file on Dropbox?

Any help is greatly appreciated.