Turn Old Zyxel USG20 To Manageable or not Network Switch ?

Dear all,

I am searching for a good alternative, and then, 
How to turn Old Zyxel USG20 (for instance) into a manageable Switch ? Or non Manageable.

The idea is to recycle and give another life to these old product.

And then, yes of course, How to Use add Wan Port ?

So many thanks for your help in advance.