Both the US and EU RoM websites have the new Chapter V installation files ready to go. (Client download link:
http://us.runesofmagic.com/us/downloads,client,us.html )
I downloaded both the full and slim clients (slim for reference purposes) and installed the full client over my existing and older/patched Chapter IV installation. For me, no hassles at all. It's (currently) one patch to game start, and the Chapter V files fix the "flickering water" issues that people had seen and reported for ponds, lakes, and streams.
I do recommend a wired connection for the download, just to avoid possible packet drops over wireless. More reliable and faster, too.