actually you are better keeping your existing arrangement .... untill the 50 (....50?????) develops problems.
use the 50 for system and core prog files (office and a few essentials) use the 500 for photo/music/movie storage
and to install games
(most progs ask where you want to install to ..... just change it to D:
you can even move my documents (right click | properties)
In your case .... look through the 50 .... find data (docs, tunes, movies NOT program files) and move them to the 500 .....
and then in future install all games etc to the 500