How to cancel storage plan subscription?

Excuse me, I looked over the word "storage", so I guess this concenrs the icloud storage plan?

iCloud storage upgrades and downgrades - Apple Support

Downgrade your iCloud storage plan

You can decrease your iCloud storage from your iPhone, iPad, iPod touch, Mac, or PC. The downgrade takes effect after your current monthly or annual subscription ends.

If you downgrade your storage plan and your content exceeds the storage you have available, new photos and videos won't upload to iCloud Photo Library and your devices stop backing up to iCloud. iCloud Drive and the other apps that you use with iCloud won’t update across your devices. You can't send or receive messages with your iCloud email address. Learn how to manage your storage by deleting backups, documents, photos, and email messages that you don't need anymore.

If you cancel your plan or you don't renew it, you'll automatically go back to 5GB of free storage.

You don't have access to an iphone I understand. Then you can either:

On your Windows PC

1. Open iCloud for Windows. (If not installed yet, download: Download iCloud for Windows - Apple Support
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.

Other option is to call AppleCare. They can end your subscription for you as well.

View, change, or cancel your subscriptions - Apple Support

1. Open iTunes.
2. If you’re not signed in, sign in with your Apple ID. If your Mac has Touch ID, you can use it to log in when you're asked for your password.
3. From the menu bar at the top of your computer screen or at the top of the iTunes window, choose Account > View My Account.
4. Enter your password or use Touch ID, then press the Return or Enter key on your keyboard, or click View Account.

On the Account Information page:

1. Scroll to the Settings section.
2. To the right of Subscriptions, Click Manage.
3. To the right of the subscription you want to manage, click Edit.
   If you don't see a subscription but are still being charged, make sure that you're signed in with the correct Apple ID. If so, you might have subscribed directly with the provider and not through iTunes. In this case, contact the content publisher or app developer directly to cancel your subscription.
4. Use the options to manage your subscription. You can choose a different subscription offering, or click Cancel Subscription to cancel your subscription. If you cancel, your subscription will stop at the end of the current billing cycle.

That should do it!