OK, say you have a product and you only have one of them when you make your new shop.
Someone comes along and buys it and now it is shown as "sold out" on your shop.
Then you get some more of that identical product, say, 15 pcs. in stock.
How do you change the product information to remove the "sold out" sign (because they are back in stock ?)
I have tried all kinds of settings in all three options of the Quantities field (right hand panel on the product's settings), e.g.
Use Range; 1 to 15
and Let Buyer Choose

but in the right-hand panel under Inventory, it still says e.g.
SKU: SKU_00000053
Set: [blank]
Remaining: 0

"Publish Product" is also set.
I've saved everything a dozen times, but the item is still being shown as sold out.
I have three such items. For two of them I have simply made a new product and deleted the old one, but I would like to know how to do it before making a "new product" for the third item.

Enter the number you want made available in the Set box and republish your shop.

Ahaaaaaaa!!! I checked in the pdf manual but couldn't find out what that Set box was for. I couldn't find help looking for the word Quantity either. Maybe that information could be added in a future version of the manual.
Many thanks !