You need to:
1. Download the full BD 4 installation program.
2. Run this and select "Remove Installation". This will get rid of whatever's there at the moment.
3. Re-run the installer and install BD 4.
4. Download the latest BD 5 update (a ZIP file) and unzip it into the BD 4 installation folder, overwriting all the files with the same name.
That will give you an up-to-date, hopefully fully-functional, BD installation.