You can upload content from your computer to easily
  update a content item in the library. You can perform this task on a locked
  or unlocked library item.
    This task assumes you are in the library of the desired
    site.
    To check in an item you perform this task in the I'm
    Editing view. This will upload the new version while releasing
    the lock on the library item. You can also use this action on an unlocked
    content item to update it without first downloading it to your
    computer.
    - 
        Navigate the library to locate the content item you want to
        update.
        Note: Click I’m Editing in the Documents section of the browsing pane to view the content items you currently have checked out.
 - In the item list position the cursor over the item you want to update to display the available actions.
 - 
        Click Upload New Version.
        
The Update File page appears.
 - Click the browse button.
 - 
        Locate the file on your computer that you want to upload and
        click Open.
        
The selected item appears in the list. Click Remove to delete the item if necessary.
 - Indicate if the revision is minor or major.
 - In the Comments box type any information relevant to the updates.
 - 
        Click Upload File(s).
        
An indicator informs you of the upload progress. When 100% appears beside the file you can proceed.
 - Click OK.
 
The dialog box closes and the item is updated. If you updated a
    checked out item, it is removed from the item list in the I'm
    Editing view.