To post a new version of a proof that was reviewed and sent back with changes, just log in to inMotion and locate the proof in your Proofs Workspace. Click the +Version button, then click Get File. Select the new version you want to upload. You don't need to label it, the system will keep track of which version you are posting. Once it uploads, you can click Release Now and it will go out with the previous settings and you're done.
If you need to make changes, click the View/Edit/Release button. This takes you to the Summary page, where you can edit the sections as needed. When you're done making any edits, click Finalize. An email notice will be sent to your reviewers and you will be taken back to Proofs Workspace. The status of the proof will change to Out for Review.