I need more storage. I’m paying $.99 for 50 GB, but I need more storage. What can I do?

See this Apple article: Upgrade to iCloud+ -> to iCloud+ - Apple Support

Go to Settings -> tap your Profile

Tap iCloud 50 GB

Tap Manage Account Storage

Tap Change Storage Plan 50 GB.

Then tap 200 GB or 2 TB

From: How to switch to a different subscription plan - Apple Support

Change to a different plan using an iPad or iPhone:

1. Open the Settings app. 

2. Tap your name, then tap Subscriptions.

3. Tap the name of the subscription that you want to change.

4. Tap See All Plans, then follow the onscreen instructions to complete your purchase.

For other devices, read the support article.