How can I delete part of my storage?

If you are talking about iCloud storage, see -> Related Article -> Downgrade or cancel your iCloud+ plan

You can downgrade your iCloud storage.

Check -> Go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.

If you have an iCloud subscription, you will receive a monthly bill from Apple, check your email box.

You pay monthly for iCloud storage.

The subscription runs as long as you don't downgrade.

You cannot deactivate/pause the subscription for 1 month, but you can downgrade to free (5 GB).

To reduce your iCloud, see also -> Manage your iCloud storage

Manage your iCloud storage - Apple Support