Every Apple user is entitled to 5GB of free iCloud storage. It can be upgraded from any device if you need extra space.
On your iOS device
Go to Settings -> tap Your Name -> iCloud -> Manage Storage or iCloud Storage.
Tap Buy More Storage or Change Storage Plan.
Chose a plan that fits your needs.
Tap Buy -> follow the onscreen instructions.
On your Mac
Go to Apple menu -> System Preferences -> your Apple ID. On macOS Mojave or earlier, you don’t need to click Apple ID.
Click iCloud.
Click Manage in the lower-right corner of the window.
Click Change Storage Plan or Buy More Storage. Here you can choose a suitable plan.
Click Next -> enter your Apple ID password.
On your Windows PC
Open iCloud for Windows.
Click Storage -> Change Storage Plan.
Choose a suitable plan -> click Next.
Enter your Apple ID password.
Click Buy.
It's good to know: iCloud storage is not intended to be used as a substitute for your local (internal) storage on your iOS device. So, if you receive a message that your iPhone is almost full, buying more iCloud storage doesn’t solve that problem.
Good luck!