Apple gift card to buy more storage

Follow the procedure in here:

Buy more iCloud storage - Apple Support

It will use the same form of payment that other purchases use: if you have sufficient store credit from having redeemed a gift card, it will be used, else the charge will go to your credit card.

If you mean can you use iTunes or App Store gift cards (not Apple Store gift cards, they are only for use in Apple's shops) to pay for iCloud storage upgrade then you should be able, I do on my account