How can I manage my icloud to gain more storage space without paying for more storage space?

Open icloud and manage your files and data -open and delete unwanted items and photos

Method 1. Delete Old Backups
1.Click Setting on your device > Find iCloud > Choose Storage.
2.Tap Manage Storage > Click your iOS device > Click Delete Backup.
Method 2. Delete Photos and Videos
You can free up lots of storage by deleting the photos and videos that you no longer need, because they are taking up the most of your iCloud storage.
Method 3. Manage iCloud Drive
1.Click Setting > Find iCloud > Tap iCloud Drive.
2.Turn off the green button to remove the files. The Mail cloud be your most consideration as it occupies too much storage.
For more detailed steps to manage iCloud storage, you can visit
How to Manage iCloud Storage on iPhone/iPad/iPod

Here are some methods to help if you don't have enough space on iCloud.

Method 1. Delete Photos/Videos from iCloud
One of the biggest data hogs to take up your iCloud storage space is the photos and videos. iPhone/iPad will automatically back up all your videos and photos to your iCloud. Therefore, deleting photos and videos from iCloud will free up iCloud storage a lot.
1. Tap on Setting > iCloud > Storage. Then tap on Manage Storage.
2. And then tap on This iPhone.
3. Under the Backup options, you will see Photo Library option, set the slider to OFF position.
4. Tap on Turn off & Delete to delete all photos and videos from iCloud.

Method 2. Delete Data & Documents
If you still find that there is no enough storage on your iCloud, you can try to delete these app-related documents and data to free up iCloud storage.
1. Go to Settings > iCloud > Storage > Manage Storage.
2. Select an app under "Documents & Data".(The first one genrally takes the biggest storage)
3. After selecting the app, tap the "Edit" tab in the upper right corner and then select the specific document to remove, or tap the "Delete All" tab.

Method 3. Close Unnessary Backups for Apps
If there are entire apps that you don't need to backup, you can do so by following the steps below to fix not enough iCloud storage for your iOS devices:
1. Go to Settings > iCloud > Storage > Manage Storage.
2. Select the device you want to manage the backup for.
3. Under "Backup Options", toggle apps off that you do not want to sync to iCloud.

Some other guides will be introduced in the following article. Please feel free to check them out.
How to Fix Not Enough Storage on iCloud for Your iPhone iPad