File => Open
select the drawing
Double click the filename under Name
Browser for your r4 and select it by double clicking it or select it and select open
Close the drawing if it's open, then go to File > Open and Browse to the drawing, select it but don't open it, and click on the References button. That will bring up a dialog box where you can link to the file.
The next time you want to change a file name I'd suggest either using SolidWorks Explorer, or, if you have it installed you can change it in Windows Explorer with the right-click drop-down. Either of these methods will update the links in most cases.
Use PDM to control revision levels, that way you don't need to create another file for new revisions, just use the same file and pdm (vault) keeps the history.