I deleted CS4 because I have CS5 also and now some necessary files are missing. Any advise???

I recently deleted CS4 because I had CS5 also on my imac.  Now it says I am missing files in the adobe application support folder to run photoshop.  It says to run the photoshop installer and re-install photoshop.  I ca not find the installer anywhere to re-install.  I purchased it via download a while back and have no information on it.  Does anyone have any ideas or advise that would be helpful?  I would greatly appreciate it.

Sincerely,

Kim