Before you pay Apple for more Cloud storage check and see what’s using up yours. On your iOS device go to Settings, Tap your Apple ID account at the top of Setting, Tap iCloud, Tap Manage Storage and review what’s using yours.
If you don’t need some some of the information Tap on it and select Delete. Once done you can NOT get this information back.
One of the biggest users of data is iPhone backups (personally I back up to my computer). Another data hog is photos and videos. If you have them already in iPhoto or Photos you can safely delete them.
If you just need cloud storage the one of the best rated and least expensive is Backblaze, you can try it for free: Backblaze