Hello, How can I reduce my Backup size?

Backups to where? If to iCloud, you can enable syncing services such as iCloud Photos which means those items won't be part of a backup. However, they still will still take up space in iCloud outside of a backup so you aren't really gaining anything other than a rearrangement of what's where. If you do this and backup to a Mac then what's put on the Mac will be less because the photos will be in iCloud.

Manage your iCloud storage - Apple Support

So in the end it really helps to have more details on what you hope to achieve by this because the answer probably has nothing to do with the changing the size of backups.

Something to be aware of is that there's no setting that will exclude all your iMessages from your iCloud backup. If your message retention is set to keep all messages, your iCloud backup size will just keep growing... I eventually discovered this when my "Next Backup Size" became larger than my iCloud storage size so the backups were failing.

To work around this, there's a couple of useful settings:

Settings -> General -> iPhone Storage -> Messages

• Auto Delete Old Conversations
• Review Large Attachments

Settings -> Messages -> Message History

• Keep Messages (e.g. 1 year)

Try this -- finally solved it... User Friendly Apple, just had to Hunt through menus forever....

Check the size of backup at APPLE ID -> iCloud -> Manage Storage -> Backups -> Backups (phone name) -> "Next Backup Size"

you may find one application hogging all the space (I did, my Drone APP, 23GB)

You can force a manual backup under

Apple ID-> scroll down to "(phone name) -> iCloud Backup (on) -> turn iCloud backup ON and use "Backup Now"