cannot upgrade my storage

If you are talking about iCloud storage, see -> Upgrade to iCloud+ : Upgrade to iCloud+ - Apple Support

⤵️

How to upgrade on your iPhone, iPad, or iPod touch

1. Go to Settings, then tap your name. 
2. Tap iCloud, then tap Manage Account Storage or Manage Storage. Or scroll down and tap Upgrade to iCloud+.
3. Tap Buy More Storage or Change Storage Plan.
4. Choose a plan and follow the onscreen instructions.

See also:

iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support

Manage your iCloud storage -> Manage your iCloud storage - Apple Support