Best option is by using JUNCTION.EXE on Windows to symlink folders on C: to F:

1. Create a folder called iTunes on F:
2. Open Command Prompt (enter cmd at Start > Run).
3. Type 'junction C:\<existing iTunes folder> F:\iTunes

Once done, u can move files from C: to F: and iTunes will find the new drive automatically.

However, ensure iTunes is not running before u do this migration.