C Drive Space Optimization

I am dealing with a problem where my Windows PC's C drive is full, even after I've deleted a large application - iTunes that comprised 90GB. However, the deletion hasn't cleared up space on the drive as expected.

Here's a quick overview of the issues :

• Primary problem: My C drive is at full capacity.
• Main space consumers: The applications on my PC are primarily responsible for consuming the most space on the C drive.
• Specific Application: iTunes was identified to be taking up a significant amount of space.

I'm looking for a freelancer skilled in system optimization, file management, and Windows OS. Your tasks will include assisting in deleting unwanted files securely from the C drive, freeing up space, and potentially reallocating space from the D drive to the C, if necessary. Any prior experience dealing with similar projects would be a bonus.