Almost two months back, Google has made available 64-bit version of Chrome on Canary and developer channels, today, it is available for Windows 7 and Windows 8 users on Beta channel, you can download it from here. You can install Chrome 64-bit Beta right over currently installed Chrome without uninstalling it, fret not!, All your settings and bookmarks will be preserved. 

64-bit Chrome for Window 7 and Windows 8 is now available on Canary and Dev channels

Download Chrome 64-bit Beta for Windows

64-bit Chrome offers more speed, security and stability when compared with 32-bit one.  You can see full list of changes in the SVN log. After installing this version, confirm version you’re using by visiting Chrome://version page, and check the user agent line on it.

Source: Chrome releases blog