How do I add a new file revision to a document?

To add a new file revision to a document you will:

Find the document you would like to edit in the Documents page
Click "Check-Out" in order to "lock" so others cannot edit the same document.
If not already on the edit page: click "Edit" to bring up the document edit page
Choose an existing revision to make the current revision or click on the "Choose File" button or drag/drop file to upload a new revision.
Add a revision comment if applicable
Make any other adjustments and then click "Update Document"
When you are done you must click "Check-in" in order to "un-lock" the document which signals the system that you are done.
The new revision will either enter into an Approval Workflow, or will become immediately active if there are no Workflows configured for your company.