Can I buy more memory.

Hi dagmar,

The link below has the general information you need about different kinds of "storage", how to get more, or how to better manage what you have:

What's the difference between device storage and iCloud storage? - "Learn the difference between your device and iCloud storage, ways to manage your space, and where to buy more if you run out." Click here --> https://support.apple.com/HT206504

Storage on a device is fixed and cannot be changed other than by buying a different device. You can use iCloud storage to free up space on a device, as outlined in the above article. You get 5 GB for free but if you're in serious need of more storage then there are subscription upgrades.