You are sign in here . . . with your Apple ID & Password (?).
Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.
You can’t merge multiple Apple ID accounts.
See -> If you can't connect or sign in to iCloud
If you can't connect or sign in to iCloud - Apple Support
Then see this Apple article: What to do after you change your Apple ID or password
What to do after you change your Apple ID or password - Apple Support
Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.
When you want to downgrade iCloud subscription, see this Apple article: Downgrade or cancel your iCloud+ plan
Downgrade or cancel your iCloud+ plan - Apple Support (PH)
The iCloud + subscription will be terminated depending on the start date.
If you start on August 1 and are going to cancel now, the subscription will stop on November 1, a monthly term is used.
If you have downgraded iCloud storage, it would take about 1 to 3 business days in order to process.
Once your request is approved, you should receive an a message from Apple in your email box.