how do I cancel itunes on a computer

iTunes is a free application, and has no associated subscription itself.

If you mean cancel an Apple Music subscription, follow the steps here: Manage your Apple Music subscription on your iPhone, iPad, iPod touch, Mac, PC, or Apple TV - Apple Support

There is no charge for iTunes (or an iTunes icon) on a computer or iPhone. If you are being charged monthly for Apple Music (or anything else) see the instructions in the following link: View, change, or cancel your subscriptions - Apple Support

iTunes is free, you cannot be paying for something that is free. Having the icon on your computer does not mean you are paying for anything.

iTunes the application does not have any cost associated with it. Nothing for you to be paying.

If you are paying for something, it is not iTunes, as said, it could be an Apple Music subscription. The steps to cancel that have already been given.

If you have a subscription for something else that you are paying for through your Apple ID, then you can cancel it by following the steps here: https://support.apple.com/en-us/HT202039

Beyond that, how do you know you are paying for something? Where are you seeing this charge? Does it say its for something specific?

See the following: View, change, or cancel your subscriptions - Apple Support

Not sure what you mean. What exactly do you want to get rid off?

The Music App?

Are you paying for something you want to stop?

What exactly is happening?