Managing unused app images

Hi, I've been using Nextcloud app on Scale (latest version installed) for a while now and relatively happy with the setup. Two things I'm still not clear about though still:

A) at every update, there is a proliferation of images hanging around. Its eating up space. It the only way on removing these still with

docker prune
In the terminal or is there a neater way?

B) how do I safely backup the whole app setup (i.e. I don't want to lose all my next cloud setup)? Say I want to move the setup to another Scale machine. Surely its not a matter of simply copying over the ix folder and the data folders?