Hey adrivargas,
We understand you need help downgrading your iCloud storage plan, but not seeing the option you need. We'd be happy to help out.
To get started, it's not entirely clear which device you're attempting to downgrade from, however if using an iOS device, check out these steps:
"How to downgrade or cancel your iCloud+ plan on your iPhone, iPad, or iPod touch
- Open the Settings app.
- Tap your name.
- Tap iCloud.
- Tap Manage Storage.

- Tap Change Storage Plan.

- Tap Downgrade Options and enter your Apple ID password.

- Choose a different plan:
- To downgrade your plan, choose a new storage amount.
- To cancel iCloud+, choose the free 5GB plan.
11. Tap Done. If you can't tap Done, make sure that you're signed in with the same Apple ID that you use for your iCloud+ plan. You can also try following these steps on a different device. If you still need help, contact Apple Support.
If you downgrade or cancel your iCloud+ plan, the change takes effect after your current subscription billing period ends."
All this and more is available at the following link which also has the steps to do so from Mac or PC too: Downgrade or cancel your iCloud+
We hope this helps out.
Take care!