Currently if you want to upload a new version of a document you need to click "Actions" -> "Edit" -> "Save".
It would be slightly faster if you had a simple way for doing this. "Actions" -> "Upload New Version" ==> Modal box opens where you pick the file and you're done.
Or perhaps even better yet, download and upload could be added as separate buttons next to Actions menu. This would reduce the time it takes to work on document versions.