How to make changes to document that was shared to me

Hi

I was granted 'Read,Write' on a document that was shared to me. I downloaded the document that was shared to me on my local drive, made changes. When I tried to upload, the only place I can upload to is my own folders. I want to overwrite the document that was shared to me so that others who have been granted access to that shared document can also see my changes. How do I do this?

Thanks
Angela