Yes, you can delete old backups you don't need anymore to clear up some space in iCloud:
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Delete backups and turn off iCloud Backup for your device
You can delete old iCloud backups for the device you're currently using, or older devices you may not use anymore. iCloud backups are available for 180 days after you disable or stop using iCloud Backup.
iPhone, iPad, and iPod touch
- Go to Settings > [your name], then tap iCloud.
- Tap Manage Storage > Backups.Â
- Tap the name of the device whose backup you'd like to delete.Â
- Tap Delete Backup > Turn Off & Delete.
When you delete a backup, it also turns off iCloud Backup for your iPhone, iPad, or iPod touch.
Mac
- Go to Apple menu   > System Preferences > Apple ID, then click iCloud.
- Click Manage and select Backups.
- Select one of the device backups, then click Delete. If you want to turn off Backup and remove all backups for that device from iCloud, choose Delete when you're asked to confirm.
When you delete a backup, it also turns off iCloud Backup for your device.
Windows PC
- Open iCloud for Windows.
- Click Storage.
- Select Backup from the items listed.
- Select one of the device backups, then click Delete. If you want to turn off Backup and remove all backups for that device from iCloud, choose Delete when you're asked to confirm.Â
When you delete a backup, it also turns off iCloud Backup for your device.
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copied from: Manage your iCloud storage - Apple Support
