How do I change an item's quantity, package size or details?

The quickest way is right in the open list: swipe the item all the way from right to left in one motion — that opens editing immediately. In pon this quick full-swipe gesture is deliberately „Edit“ rather than „Delete“, so a single swipe hits exactly what you need most in everyday use. In editing you can change quantity, package size/pack, attributes, price, offer, image and note.

If you just want to quickly change the count, swipe a little less far to the left and tap „More“ — there you'll find a large quantity slider, the tiles Copy, Move, Edit and Delete, and at the bottom the „Mark as bought“ button that checks the item off right away.