- Close running instance of Reaper (v6.05) in your case.
- Download new installer for your OS (also correct architecture 32/64 bit)
- Run that installer.
- During installation, navigate to the same folder where your 6.05 is already installed (maybe it will be set correctly itself by installer, but double check before proceeding, to be sure).
- After installation is done, let it start.
- You have new version (and your preferences "should" be preserved)
Hint: It is always a good practice to backup before doing anything new, of course. So maybe, export your Reaper configuration before updating at least)
It's in
Preferences -> General tab -> Export configuration..." button on the right.
EDIT: He he, it took me some time to put the words together, so that toleolu was quicker