Can I “reset” my iCloud backup?

• No, deleting a Backup will not delete anything off your phone.
• Yes, you can delete your backup. It may take a minute to see the iCloud storage freed up and you will need to back out of settings and go into iCloud again to see it updated. This also turns off iCloud Backup on your device, so you do need to turn it on again.
• Any photos/data that were unable to sync because there was not enough storage space previously will quickly fill up any space you free up.
• 50 GB is a lot of data, so I don't know if that is mostly from photos/videos or app data. I am sure your have gone through Settings > [name on top] > iCloud > Manage Account Storage to view what is using your storage, but you may have to make some tough decisions on if there is anything else you can remove from iCloud Storage or if you need more storage space. If you are seeing a lot of storage use from Photos (and I assume you are using iCloud Photos), then you will want to go through your Photo Library to see if there are any Photos/Videos that can be removed. When I take a picture, I take 3 or 4 of the exact same thing, when really I only need the one good one. That could do a lot to free up the amount of iCloud storage space you need, although if you find yourself always bumping up against the 50GB wall, then it may be best to purchase the next tier plan.

Are you paying for the additional iCloud Storage?