How do I cancel my Icloud extra storage on my pc

Cancel upgraded iCloud storage by downgrading to the free 5GB plan. See instructions in: Downgrade or cancel your iCloud storage plan - Apple Support including the following:

Downgrade or cancel on your Windows PC

1. Open iCloud for Windows.
2. Click Storage.
3. Click Change Storage Plan.
4. Click Downgrade Options.
5. Enter your Apple ID password, then click Manage.
6. Choose a different plan.
7. Click Done. Can't click Done?

and another option is:

• If you don't have one of these devices, contact Apple Support to change your iCloud storage plan.